Another idea, though this one is fairly complicated and probably not worth the effort.
I was hoping there might be a way to make enemies calculate stat bonuses gained from weapons when attacking. Fior example, if I have Luce which has a 0 in MGT but a +25 gain in the MAG stat, VS a Fire tome with only 1 MGT and no MAG bonus, the enemies only choose to use the Fire tome because they don't see the +24 damage that Luce has over the Fire tome, see? This includes missing out on other stats that could be boosted, like HP, DEF, RES, SPD, etc.
Dunno how you'd solve that issue, but there's the suggestion anyway.