FFXI also allows all classes on a single character. A few other games do as well in their own ways, though it's an unusual feature to be sure.
The right way to do the glamour system would have been to encode it as part of the individual gear sets.
So gear set 1 contains its 14 items, helm/weapon/visor settings, and glamour information. Gear set 2 contains a different set of information that is not dependent on gear set 1 in any way. This would eliminate the need for glamour plates, although you could still do that system where you just make the glamour plates temporarily override (but not overwrite) the gear set glamours.