But the "general monster sprite" doesn't look as nice as normal ones.
In Sylia for instance, iirc, there were different monster sprites, but each sprite represented a group of monsters - unlike LF, where every sprite was one monster, and when you killed a whole bunch of them, then all the sprites were gone. So you'd have to have various sprites running around in order to have different monsters in one group. Which is very repetetive when levelling up. Every time you return to the screen you fight the same group again.
In TBOL every dungeon has several different groups of monsters. That's why I said it's not as boring to level up that way.