Are our themes poorly designed?

I think you may be conflating two separate problems. Themes may be bad for two reasons: Either the models that make up the theme are suboptimal, or the theme itself is poorly designed. 

IMO, call of the wild is the first issue. Yes, it could use an in-faction unit (and kuririnad I can't think of another factions' jack or beast theme that doesn't allow at least one mainline faction unit in addition to jack/beast support) but the main issue is that our stable of living beasts is crap. The only living heavy that I'd say is in a good place is the pureblood, which is more of a support heavy than a beatstick, and the vast majority of our lights...suck. The theme benefits are fine, and while I personally think it's shitty that we're one of the few factions without a 'combined BG models theme' (the other being Retribution) I can also see that the theme benefit is better to make up for that (-1 cost on animus is pretty damn sweet). Buff beasts, and call of the wild becomes very reasonable. 

Wild Hunt is some of both. Lots of wolf-sworn models aren't particularly strong, and while ambushing wolves of orboros are good, it's more a case of fixing a not-very-good base unit, which is never as exciting as buffing a unit you would have taken anyways. Similarly, tracker is both A) a bad theme benefit, because terrain layout can easily mean your theme benefit does nothing and B) TERRIBLE with the non-pathfinder living beasts we seem to be cursed with. 

My suggestions: Replace the tracker benefit with 'warbeasts gain gang fighter'. There's precedent for it in slaughter fleet, and it would play into the cooperative theme that the wolf-sworn have going for them - little wolves of orboros helping the big wolves pull down prey they couldn't handle without the help. 

Drop the Wolves of Orboros UA to 3 points, allow death wolves to start with one corpse each (this also helps open up Devourer's Host) and give Skinwalkers +1 speed and armor and straight up pathfinder to let them operate as an actual tarpit unit. 

Allow Wolf Lord Morraig to be taken free in-theme

Secret Masters is just...the worst, on so, so many levels. The theme benefits are skornergistic (you get free points for blackclads, but you are encouraged to take minions to gain the benefit of sac pawn, but minions don't count towards free points...and you can only take one minion unit anyway). The free upkeeps benefit is not very impactful (we have two casters that typically have trouble with first turn upkeeps, and only one of them is allowed in this theme) and the warlock restriction (which is nonsensical) prevents several casters that might actually want to use this theme from doing so. 

On top of that, the very concept of the theme is off - similar to sons of the tempest, it's a theme based almost entirely around support models, except unlike ATGM, druids can't even kill single-wound infantry well. They are a pure support unit, but the theme seems to want to take multiple units of them as mainline infantry. Maybe releases somewhere down the line fix this (though a martial blackclad unit just seems...off to me, from a thematic standpoint) but for now it's just a mess. 

On top of THAT, blackclads in general are not particularly good. Mist Riders are...acceptable at what they do, but expensive and inflexible. Druids are just the worst, having lost nearly all of their utility going into Mk3. So there's really very little incentive to play this theme, outside of certain janky builds. 

My Suggestions:

- Allow any number of minion units to be taken in theme.
- Allow one minion to unit to become friendly faction.
- Free models: 1 free model for every 20 points of FF units or battle engines
-(Wishlist): remove free upkeeps clause, allow one minion warbeast to be taken by a blackclad warlock.
- FIX Firetrucking druids of orboros. 

Another thing I dislike about our themes is how restricted druids are (and yes, I know I said they're shitty). We are playing Circle Orboros. Druids ARE the Circle Orboros. The base unit of druids should be available in every theme. I CAN see an argument for not having them in Devourer's Host (Tharn are kind of their own thing, and seem to be more 'allies' of the Circle than vassals (like the wolf-sworn) or the beast themes). 

I think a large part of the issue isn't the themes themselves, but that currently the quality of models within certain themes aren't up to scratch. The only exception I feel is Secret Masters which is simply terrible since the benefits AND the models are just awful. Using Bones and Devourer's Host as examples:

-Bones
They had a mini CID already so most of the core pieces function as intended. While a few outliers exist (Woldstalkers are the big one for me) it can be built as either a melee based armour cracker under Bradigus, an attrition monster with Baldur2 or a combined arms build that brings multiple tools to the table - eKrueger or Baldur1 spring to mind. While not perfect it shows how a well designed theme has lots of variation in how it is played and built based around the Warlock.

-Devourer's Host
I've tried it exclusively with Una2. Personally I think she does the most for it and gives it dedicated direction as an anti-infantry build while bringing a reasonable battlegroup that can deal with most armour. I've also seen it being taken with Krueger 1, Baldur1 and I can see a case being made for Wurmwood running it effectively. However I see a theme (no pun intended) with all 4 of these Warlocks - they protect them on the approach. While the build itself is designed to mulch infantry they simply don't arrive without Warlock support when running into guns. And while dedicated gun-lines seem to be less common, my experience into even combined arms lists has not been very successful. I feel that while this theme can handle some very specific matchups, it also has a lot of weaknesses. Fortunately one of the matches it is pretty great into is the Witch Coven which immediately makes it worth considering as a pair for anything. My hope is that the Tharn CID will make them a little bit more sturdy on the approach and hit a smidgeon harder when the remnants of the unit arrives.

With regards to Wolf Sworn and our living heavies it's pretty obvious they need tweaking. Comparing our new and shiny 14pt heavy to a 17/18/19 point Warpwolf shows that disparity pretty heavily. The Wolf Sworn probably don't need tweaking too much but the theme benefits seem contradictory - Take WolfSworn for free points. And Warbeasts gain Tracker. But your living beasts don't actually have Pathfinder!

If you want to be technical none of the Griffins have it either. Though I think the point stands that if you want to kill something with living warbeasts that's on the other side of a forest and you have no teleport available you usually aren't gonna get the job done.

x.O; wow, talk about raining on a parade.

Bones may not seem to have great benefits but, in reality, I have yet to see someone lose while using it. With theme, it provides a perfect balance of overall scenario pressure and both attrition as well as armor cracking.

Call of the Wild requires the appropriate casters, yet some of the lists I've seen are just ridiculous. If/when the warpwolves get their point costs reduced by 1 or 2, you'll be seeing it as quite the murderous theme.

Devour's Host is the kind of list most factions would fall in love with. "yeah, I'm just going to take my regular list and give all the beasts RFP and healing. Oh, and that thing that lets me chain kill entire armies? yeah, I'm gonna get to distribute a few of them freely now. enjoy ^-^"

Wild Hunt... needs work

Secret Masters... incomplete

It is always a bother when people complain about receiving presents they didn't ask for.

For the opener-

I'd need to see your list of possessed models before I could just spout out what you need next. For right now, bones is definitely our strongest choice, but it's assassination potential really isn't the best. Put the shifting stones as high up as possible with a wold guardian directly behind them. First turn, run the wold as far up into the shifting stone triangle as possible. Then activate the shifting stones and teleport the wold an additional 8 inches. With 20 arm and plenty of boxes, you'll have plenty of contention right off the bat and force the opponent to come to you. The Devour's Host lists I've seen run strong off of heart eater chains to clear the masses with more powerful beasts for a backing. All lists that aren't bones will need 2 wild argi. If you want to go into CotW you really need to open your inventory of beasts and see how each one works in tandom with the others.

For Others- 1 razorwing w/primal and synergy (kaya3) or Forced Evolution (kaya2) trampling across a field. figure out the average damage per model on a unit of trollkin champs...

a cheap get would be a sentry stone along with a caster or two. You'll have to pile on a LOT of cash if you want to go the bones route, as nothing but the shifting stones and wayfarer are eligible for it. I'd hold back on the reeves for now, same with the skinwalker UA. Instead, focus on Devour's Host. Kromack 2, ghetorix, stalker, pureblood, gorax, wild argus or two, shifting stones, the path you're taking for getting models would probably be best to focus on tharns until you save up enough to start buying into wolds. For now, keep your eyes out for wolf riders and their solo, Tharn Ravagers + attachment, Tharn Shaman, nightwitch, and bloodweavers.

Wolfriders are super fast getting up the board and have pow 9 weaponmaster assault shots. With their solo, they can also hit reliably too.
Tharn Ravagers have the heart eater advantage, but when they have their attachment is when it shines. With the attachment, they all gain overtake (move 1 inch after killing an enemy model) So every time you kill an enemy living or undead model you can move 1 inch and use the heart from the enemy you just killed to buy an additional attack... and then chain it. every single one of them work that way so you have a lot of chances for huge chains.
The bloodweavers are a little more on the weak side, but they are our assassin styled unit. Once they kill something, they can make it "pop" and hit everything within a 3 inch AoE take a pow 8 blast damage roll. With the nightwitch, they gain killing spree, which is basically the exact same thing as the Ravager's chain kill.

The reason why I noted that you probably shouldn't go for bones yet... 4 heavies, 4 lessers, 3 solos, 1 battle engine, and a new caster would be the minimum of your purchases... so around $375-425 USD and that doesn't include if you want to go the garg route.