MTB helps balance, a lot, and the braking technique/ability is more refined, but MTB'ers are not used to racing next to other riders, and this is often apparent. As a road/track rider who has done some MTB cross-country races in NorCal in the last few years I noticed these things, as well as the relatively unsophisticated tactics among the sport level riders. It also seemed like the level of fitness was lower in those races than what I generally see among the road and track racers of similar category, e.g., expert=cat2, sport= cat3, not quite.

But c'mon, even if you aren't doing MTB races it's a lot of fun to play like a kid on a bike again! And 20+ mph between the trees and over the bumps is rejuvenating.