I only encoutert the fire nation 2 times in Rpve 9 4 players yet, but i really liked what you pulled togehter. I encoutert the Fire Dancer Boss and she seemed to use spells with a Plan? She uses Global Warming against my ice shields and i loved it! I think Bosses where decently balanced but the "normal" units could get a little buff.
My idea would be that offence is the defence of the fire Nation, so maybe make their attacks much stronger. I don´t know if this is desireble with the defence rpve "on the way" but i guess that would be fitting and make fire a lot stronger especially in the