It's not overtuned in the slightest. WHM and AST do not have access to the 5 DOTs (including Miasma 2 and Shadow Flare) that SCH has access to (6 if you cross-class Aero) so that is why the potency is slightly lower; WHM and AST rely more on direct nukes and so their nukes are a little stronger.

It's also tuned around the fact that if you properly manage Aetherflow that you will never run out of MP (unless you have to rez people or resummon fairy a bunch for whatever reason)