I don't understand why people complain about aspects of a game that's optional. If you don't want to try, it isn't an integral part of the game, so don't?
Both of the new dungeons look like they will be optional as well, and there's even an SNES mode for true purists. There's really no reason to complain. Just skip what you don't want to try.
I for one look forward to the new features of the game. The arena looks interesting (a bit like pokemon, but not completely. I've played a ton of games where monsters could be raised as a teammate or battle fodder. Hell, Neofio could be considered such, as well as Pip, from CC.)
With a collector type personality, I will likely want to grab any items that will be unique to the arena.