It's just boring doing the same thing over and over. It gets very repetitive. The games are pretty long already and I usually just want to get to the next story beat. Tokyo Mirage Sessions did it right. The dungeons weren't quite as long even with the backtracking and the combat was always fun to watch during the Sessions combos. I've been on a media blackout for P5 so I hope the combat is just as fun to watch as to play.
The TMS dungeons ended up being a pain in the ass because of all the gimmicks they threw in to make them more interesting.