3DS has better gameplay mechanics (i.e: "fixes"/"updates stuff like random encounters with monsters appearing on the main map). Main boost PS2 has is that it has slightly better colours etc. Depends on your own tastes
I haven't noticed any points so far where I got smacked back and forced to grind, with the exception of one boss (you can guess what it was if you've played), but that was probably my fault for overusing holy protection (and all I needed to do was level up Angelo enough to have multiheal)
It might be up there, but you get sooooooooo tired of hearing it over and over and over throughout the entire game. The game should have had multiple overworld themes for when you're walking which is like 95% of the time.
Also, how could it be that the first area in the game that isn't a hillside, a dungeon or a cave; comes 40 hours in?
https://www.youtube.com/watch?v=r7TBbSN7bYU