I think it depends a lot on the fighter.
Some fighters can go a long career without taking too much damage, whereas every boxer is going to get hit in every fight and in sparring. Some MMA fighters don't like to strike and are good enough to generally avoid striking damage.
But in general, the typical boxer will absorb more punches, but with dampened force. MMA doesn't dampen the force. I'm not sure if that's a good thing or a bad thing, honestly, because while they may get KO'd easier, is a KO really any better than getting hit 50 times without a KO?
All I really know is that concussions will fuck you up.