I don't care about the equipment really, without strength and offensive talents, a mage does no significant damage with that axe, and the armor is necessary due to the lack of defensive spells/traits - it's the only practical way to raise the defense on your heroes.
They actually already have a balance mechanic in place to prevent mages from loading up on heavy armor - encumbrance...
But then they break that mechanic immediately with mounts, who remove the need to worry about equipment load
The penalties for high encumbrance are also really minor (-1/-2 init iirc) relative to the insane init values heroes can acquire.
Get rid of the horse bonus to equipped weight for heroes (units may need it, I'm not sure), and change the -1/-2 penalties to -15%/-30% or something and you'd have a good reason not to load down your mage with full plate.
As for the multiple Paths... I'd be ok with restricting it only if they greatly expand each path's trait tree, otherwise you'd quickly run out of interesting levelup decisions to make, which would be less fun.