Help Me Understand How Zerkova 1 Won the Seattle Open

well for one being able to countercharge everything through your own models, with greatbears/kovniks/markov is bonkers good. crit from malakov means that attack just failed.
Zerk can deliver her army without it really taking damage with clouds, her feat can sometimes gain yet another round of nearly undamaged models. They're basically waiting until their turn 4 before they get to do anything if played right. Watcher has some very good uses as well. And well.. that many iron fangs hits real hard.
Z1 herself is spell proof which is nice, watcher is good for survivability, and she can do a lot of work on her own with the arcnode gun and frost hammer. She's also got some pretty good spell asssassination routes at times.. shes a beastie.

Something I've always considered a game winner.. getting two meaningful charges in a game with a full unit of uhlans, is very doable with her.  though jeff doesnt use them.. he likes the conquest instead, so even more denial with the creeping barrages

One of the reasons is that Z1 and Los really synergize well with each other. Ghostly is something the theme list needs desperately and the cloud wall is really good for countercharges.

Add to that the fact that most armies atm simply lack the volume of attacks to fight 40 Models( especially when they are not easily killed) plus the insane speed of the List and you have yourself a winning strategy.
The List is probably really good in scenario, attrition and thx to zerkova not bad at Assassination.

I really like the List and would try it if I had the Models

List is quite simple: it stacks denial effects and forces a lot of bad decisions from your opponent. The list can deliver itself against ranged armies using Zerkova's clouds + her feat (and Pikemen are ok into a lot of shooting naturally), but the real juice is its ability to fight back against melee armies with Counter Charge, Watcher and the Creeping Barrages from the Conquest. Simply put, if you put a line of clouds in front of the Pikemen and an opponent walks into them, they're going to be hit by a bunch of high POW counter charging solos or Bears with precision strike. Typically the Kovniks and Bears hide behind the Pikewall and then use Tactician from Markov to burst through the lines. If the clouds entry points are roughly 6" away from your counter charging models, anyone who pokes their head in is getting an Axe to the Face.

This can be further enhanced by using Creeping Barrage from the Conquest for more area denial or the threat of a Watcher'd Punch/Main Gun shot. You dangle this over your opponent as you advance up the table, especially backed up by Zerkova's feat which is a hard shut-down of almost everything in the game. The list lets her play quite aggressively too, which is when she's at her strongest since you can get some spectacular feats. 

Then her spell list helps the Pikemen out in indirect ways. Ghost Walk is pretty obvious and works well with either pikemen flavour's CA for either a free-strike dodging 5" reposition or making Sidestep actually work.Jeff has gone for the More doods approach as opposed to handing out UA's, but you can make lists where all 3 units have CA's, usually done by going 2x Max units and 1x Min and chopping up the list somewhat. In any case, without CA's you can just give Ghostly as the pathfinder answer instead of Relentless Charge. Hex Blast to provide a Rng15 or Rng 10 True Sight upkeep stripper is nice and makes up in part for Zerkova's lack of dice fixers, as is her Zerkova's combo of killing someone to turn them into an Arc Node then throwing out a 1 Focus Frost Hammer. Watcher has been discussed before, though it's more a threat than something that actually happens a lot. Still, it's a good threat.

From experience the list is a bastard to engage, especially on a central scenario it can brick up in or if your opponent doesn't have answers for Zerkova's bag of tricks. It does, however run out of steam as the game goes on: Zerkova has to typically spend a lot of focus to do any of her high-impact plays which can leave her vulnerable and you can only Feat once. Zerkova's end game is ok, but no way near as impressive as, say, Strakhov 2's running a similar list. In addition, the list becomes worse at setting up positioning traps the longer the game goes on, due to the simple tyranny of losing models, having to commit them, split them up and so on. In addition the lack of threat extenders really hurts your Colossal get to grips with your opponent: it truly is Speed 4 instead of Pretend Speed 4 like most other Khador casters can make their warjacks.

As for Uhlans, the TLDR on them is that they are bad without a strong damage buff & don't fit the list which is mostly defensive and denial in nature. They're also cost-ineffective against their intended targets. Like think about how many Uhlans it takes to kill a Marauder or a Juggernaught without something like Battle Lust (or even a Gladiator or other such warbeast). Forcing bad engages and then mobbing people with Pikemen tends to work better.
However if you want Uhlans, you can make a build where you swap the Conquest for, say 2x Destroyers, cut the mechanics and fit in a min-max unit of Uhlans depending on taste. 

A note to end with on Zerkova: she works best when positioned aggressively. She is actually one of the most difficult casters to kill in faction despite her stat line due to the sheer number of random defenses she has. Her feat is one of the strongest denial feats in the game and works best with an aggressive push...within reason. Getting her positioning right is one of the keys to playing her well given her relative lack of mobility. You want to balance the line between shutting everything down such that even a Defender cannot escape your feat and getting punched in the face by said Defender because you got a bit Tooo crazy and your opponent found a zone where they wouldn't trigger either Watcher or Counter Charge to attack you from. Given your lack of threat extension too, you have to often "buy" that by going a bit aggressive and locking people down such that they cannot either escape or meaningfully engage your models. Feating and then running the Conquest such that it's now in threat of stuff and is in a prime spot to Watcher-Punch any protesters is quite nice. 

All up it's a list that Zerkova has been lacking I think: one that feels like a good fit for her particular brand of denial.