I know it ,ight sound like an annoyance...but FF sages shouldn't come from these classes. FF sages are dark magic specialists that use mace-type weapons...they are pretty much the mage counterpart of dark knights, just like white mage is for paladin.
So sage would fit much better the position of a class that is coming from THM.
The idea of using DoH or DoL to unlock other classes would be very nice...like needing GLA+ARM to unlock Defender, BTN to unlock Geomancer, GLA+CON+BTN to unlock elementalist, etc.