The belra of the "ultimate" mode must have the strength of the "ultimate" mode and not a "buffed belra". Remember that not all players have the "best weapons"
Still, I agree that there should already be a new level of difficulty for players with good weapons. A cracked mode as they say, Super ultimate, inferno mode, Dead mode, nightmare mode, or whatever they want to call it.
But honestly if such a mode were to come into existence, I'm sure that when all the enemies of the same room are stronger (and not just the belra), all those "experienced super warriors" will come out crying from the room.