I like the 2/3rd caster approach, and honestly I would turn most casters into 2/3rd casters except wizards and cleric.
buff up EK and AT to 1/2 casters(1/3rd casting really sucks)
the you would have:
full casters: wizard, cleric
2/3rd casters: Artificer, Bard, Druid, Sorcerer, Warlock
1/2...