i'm sorry but this is horseshit development and poor writing:
"OH LOOK ALL THE SUDDEN IS THE SUPER POWERFUL SUPER READY NEW ENEMY THAT SOMEHOW HAD THE PERFECT PLAN ALL ACCORDING TO KEIKAKU KEKEKEKEK".
it's idiotic that what it is, the defenders will always have the upper hand and should have killed enough to offset the numbers with skill, they also don't have a single fucking archer/crossbowman that would take out the barrier boxes/mages holding them, in fact i have not seen a single ranged weapon that would make this a moot affair by simply sniping the "eeeevil boss"