When you say "MK does not guarantee victory", we can only assume that you're saying Snake and Dedede DO guarantee a win.
When you
assume, you make an
*** of
u and
me.
Say it with me now.
EDIT: Oh, and if you really think about it, MK is a viable answer to everything in Brawl. Why learn different characters when you can learn MK only and do even-or-better against the whole roster? MK isn't broken, but he ranges from "too good" to "perfect" at two of this game's objectives, which are "
knock your oppoenent off the stage and prevent them from returning" and "
return to the stage to avoid losing a stock". Now, couple these with his tools to answer everything, his ability to survive until very high percents (heavyweight property), his lightweight properties (ability to avoid being combo'd), and the most insane moveset in the game in terms of speed
ower (excluding Snake's ftilt and utilt, which are only 2 attacks, rather than 4+ [dsmash, fsmash, upB, nair...]), and you get what we have here: a character that people find themselves complaining about because, I repeat, is "too good" at what this game is about.
Nothing can stop me from picking MK over my mains, and nothing can stop anyone else from picking MK over everyone else. As you can see, some people don't use him because of the social consecuences of being labeled a "tier ***** (a soft ban, IMO)". If this wasn't a problem, we'd see more MKs than we have now (not saying that 21% of tourney participation is a lot, I agree that him being the BEST means he has the largest representation).