Or instead, they could simply modify the code in religion spells to make it so priests cast them at much greater levels, even than mages. C'mon, this isn't channeling normal magic, this is channeling divine might, which, hello!, priests are the masters of. Classes already influence stats, by way of deciding which two stats you can hit 50 in. As for resistance... that doesn't really make much sense. Just because you decide to be a fighter doesn't automatically make you less vulnerable to physical damage. That is illogical.