Pretty much leveling is quite fast also leveling your skills is fairly easy as long as you have what is required to raise it to the next level.
This is only true until you reach Lv100. Similarly for Tech/Arts (pre-100), if you keep rotating class/weapons/techs, Memory Fragments won't be enough. That is until you get those Promise Order from Kisara that gives you 20x Memory Fragments but that is only up to E. The PO was only added in the latest patch (150 max level cap one).
Early 100s have a very huge wall for equipment, and skills. Not to mention they have a huge annoying game balancing that becomes "bait and switch" (Glorious Rain barely increases in power while other skills' power increase is as much as 5x (or 3x can't remember) going from 20 to 21).
Naturally, that makes normal attacks much more useless post-100.
To make grinding worse, only stages with 難 can have the highest difficulty, so it limits available places. The stages I saw at low 100s were not versatile enough. >_>
As for PO giving so much EXP/etc, there were some added, but those that I have done no longer speeds up leveling in the same way that pre-100 did. Maybe the new paid DLC quests (if any) do. Maybe. >___>
I gave up around Lv-105-ish I think.
P.S. No matter what class you are, try to get Buster to 101 as it provides Tech Art JA Bonus, which gives "+80%" damage to Tech/Arts on successful Just Attack if you keep switching between techs/arts. If you're a Force/tech user, this will save you space on your skill board as Tech JA Advance can result from TAJAB + Tech Advance. They have pretty good synergy anyways.
Edit: You can always finish the main game and post-game and never bother with post-100 stuff. I think I finished most post game (minus 150 level patch stuff) around 80 hrs or something.