Wow didn't expect this silly little question to get so much attention... thanks for everyone, you truly are awesome.
Thought about it quite a bit and while the answer I like most was the one @John suggested at the comment section about them hanging with him do to it being the awesome thing to do I'm going to go with a different route, apologies in advance if some of you feels like I'm bending the question rules with this answer but I feel that this twist to the story is too awesome not to use (couldn't have figured it out without you).
dave isn't awesome... or is he? if he's just a catalyst for other people awesomeness or the baseline 0 awesomeness other people are measured by then that kinda makes him awesome,if he's just really reliable and always been there then that also makes him awesome.
In fact just about every reason covered by the answers given (which are all awesome don't get me wrong) also seems to make him just a little bit awesome when you think about it... awesomeness clocking device? just being named that is awesome... anti villein awesomeness secret weapon? secretly awesome... allow the awesome magicians to relax from all the awesomeness? everybody needs some downtime and giving somebody a well deserved rest is awesome... even having boring magic is awesome because since when is magic not awesome?
So if dave is somewhat awesome how can he suck the awesomeness out of everyone and everything around him? like @Tim B II suggested awesomeness is only awesome when measured on a scale of awesomeness and dave well... dave breaks that scale... he isn't drowning out the others awesomeness due to being so boring... he's secretly the most awesome thing to have ever existed and anything else ceases to be awesome near him.
Why nobody knows it about him and why everyone think he's so boring you ask? the reasons are tri-fold:
- Because he's confident enough not to brag about your abilities is the awesome thing to do.
- dave hiding is awesomeness is the form of playing the long game, preserving the element of surprise should the situation ever become dire enough, and planning ahead is a sign of an awesome individual.
- dave is effectively allowing the other magicians to discover their inner awesomeness like @John suggested by hiding his much more powerful awesomeness and the only way he can do that is by self sacrificing (again awesome) every bit of reputation he would get had he showed it's true awesomeness.
and why lower case "d" in his name? dave gave the upper case to charity... he's so awesome he can literally give letters to charity, and being an anonymous donation his secret is still safe.