Sorry if there is already a thread on this but I've just seen it on the front page of Overpwn and couldnt see a thread on it.
From the official forums http://us.battle.net/forums/en/overw...page=5#post-83
McCree
I've been watching McCree carefully since we've released. McCree's flashbang plays an important role in being a strong option against very fast/agile teams (tracers/genjis/etc). It is also a nice tool to prevent close range devastating abilities and ultimates such as Reaper's Death Blossom.
That said, its probably a bit too good at dealing damage to higher health targets such as Tanks and barriers. I don't have any concrete changes yet, but I'm going to be testing some things internally to see how he plays.
D.Va
D.Va's damage is definitely on the lower side, much like Winstons. They are this way for a similar reason: They are both very mobile and hard to kill. Every character in the game has strengths and weaknesses, its part of what makes the teamplay work well.
That said, I do think the is some room for some D.Va improvements, but these are unlikely to take the shape of increasing her damage output significantly.