I got my ass handed to me the first time i tried to beat sephiroth, when i was level 55. I came back at 65 and had no problems with him. So yeah, I needed some grinding. The amount of grinding was however extremely short compared to all the time i spent doing stuff that progressed the story. Didn't grind for more than a couple of hours in a game that i had spent well over 50 hours at to get to the end.

I was also a dumb teenager with no real experience with RPGs back then. Basically, I sucked, replaying the game now, I would probably be able to beat it at whatever level i got to by the end of the game.

Anyway, my point isn't that everything that is to do in FF14 should be doable the second you were done with the main story, but that the main story itself should be completable with a minimal amount of grinding outside of what was required to progress the actual storyline quests.