In fact, what breaks the balance is the temporary military buildings. These pictures speak for themselves :
This was on my live chapter 17 city, spire level 3 encounter 1. All bonuses combined, I have +122.5% health and +174% LR damage. Wave 1 was mages/HM, hence the archers. I can reach such bonuses thanks to military wonders a level 10 fire phoenix, but more importantly with 2 DA + 2 ELR. This is sustainable thanks to level 26 timewarp + level 1 polar bear that give me 82% tournament time reduction (3h/round), enough to make my 5-day boosts work for 2 tournaments and spires (with time instants for Spire, placing my boosts on Friday evening). I would never have been able to fight this in my second city, where I have a level 7 fire phoenix, am running out of UUU/DA and can't have them working for 2 weeks.
These crazy military boosts broke the game balance, but now it's too late to remove them.