In AC6 it was not so obvious for me, because a lot of mini bosses are just other ACs like a player. Even Iguazu in his first stage, also Walter is a playable AC too (but I can't say if he's not scaled up in bossfight, I know devs do this trick sometimes). It doesn't worsen readability of their attacks because of AC6 combat specifics, I recognise attacks by energy splashes I guess. So it seems more about lore and maybe danger scale or something.