As I noticed, after introduction of bosses (and boss slayers, and powerful weapons) game got overpowered enemies - and overpowered means to counter that. So in the interaction “player-boss” it’s all right.
But when we remove one part of equation - bosses - we receive almost useless troops outside of boss battles, for one (and so far it always new troop requires for each boss battle, so they even never recycled), and for two - players became extremely powerful, far over any monster. (That essentially makes quite trivial every battle that is not with bosses - or with players on both ends). I feel it slightly wrong.
What if player would count as boss? It would give new life to all this boss slayers, for one, and somewhat add challenge to all-too-simple quests, arenas and explore battles.
I would add “players as towers” effect, for the same reason, but it sounds tad silly. 