You're picking the wrong things, it wouldn't make sense to only have mp5+ as citizens or allies, that's something pretty common.
What i think should be limited is spell-casting abilities, e.g. mirror, guardian, invisibility, other army are some advanced magics that could be allowed on mp5 only, other stuff like movelock, attacklock, give vital, no armor, weaken are by far less advanced spells and could as well be allowed on mp4 imo.
Some armors, mostly Medusa and Sun God, could be restricted for MP3/4, since they are advanced gears, too.
I would even consider restricting creatures, but on