With random encounters you can make larger areas, in Chrono Trigger, most of the areas were rather small rooms with 3-6 enemies at max. Random encounters can give larger variety of enemies and surprise the player ever now and then.
Set encounters are boring cuz you know very well what the next enemy is like so you can adjust gear and everything else.
FF9 early in the game, you can get out of a grotto and encounter a dragon that is far too strong for you. I liked this surprise.
Face it, random encounters spice up the game and increase difficulty level, when you see enemies you are not surprised, and you get bored of combat quite fast.
Class system needs to return to FF games, otherwise, I can't really call them FF games much, of course there are exceptions among FFs where everything was fairly balanced, but since FF12 it was rather meh. I'ts fairly boring when everyone can do everything.