The only way a fire-based theme list is going to work is if "all enemy models have fire immunity replaced with fire resistance"
Because theres way too much fire immunity in the game right now and it would hard counter a fire-based theme way too easily.
If there can be a theme that removes Advanced Deploy, I see no reason why a theme couldn't remove Immunity to Fire. But then we start to get silly, and could have a theme that gains protection from another theme's ability to remove such things....
I think my biggest frustration in building lists is that for every single one, there's always a model that I want to add but can't. Flameguard theme? Oh hey I'd love these Knight Exemplar for hitting power but I can't... Exemplar theme? Man I'd love to have some Cleansers or Daughters for additional board control but I can't... I don't know what the right solution is, but I'm hoping for something more versatile. Perhaps a "Northern Crusade" style list would have the right combination of parts?
if you could easily destroy forests, forests would become pointless.
Burning forests are a terrain type that many people don't use or realize exists. We aren't asking for the ability to remove a forest by burning it down. Just the ability to turn it into a "burning forest."