The offense mastery isn't really overpowered when you factor in the big nerf bat they threw at the last skill attribute, combined with moving smite to defense.
our support has been all up ins for the offense tree as Soraka and Sona and they've been owning as 21/x/y. Hell, even our tanks and jungles love the shit out of that tree. And they are not dopes! The ap or ad bonuses the tree confers for laning are just way much more useful to a support than the support tree is!