What I hate most & is most toxic to the genre is stat-gains being tied to the class you're on when you gain a level.
Ex. in Tactics Ogre you could make your Mage-types OP by first leveling up a Ninja like crazy for tons of Agility... this would make their spells hit 100% of the time without fail.
Such a system is really stupid & creates a god-mode or bust scenario.
Players who min-max their stats break the game with their OP'ness while players who neglect such a forced-system or are unaware of it gimp themselves.
It's a very faulty system in general.
While it can be entertaining, it's also a very convoluted & unforgiving system as there's typically no option to de-level.