I think one issue is just how long you're stuck with specific characters. I'm 8 hours in, but only just got my fourth party member and its obvious that I'm still very early in the game (despite the fact I'd probably would have finished most current gen games in this time). I'm just used to Shulk/Reyn/Sharla, and I imagine developing that kind of play style is hard to break as new party members are slowly added to the mix.
That and I still feel like I can't get rid of Shulk, so there are really only two party slots to play with and the physical DPS role ends up being filled by him so if anyone else fills that role (even if they're mechanically different) they're still not as useful as Shulk.
I'm really hoping that at some point in the future I don't have to worry about dealing damage to Mechon.
8 hours in and you just got the 4th? God damn. I'm like 23-24 hours, and just wrapped up the Colony 6 stuff to obtain the 4th.
Shout outs to side quests adding in so many hours.