In general I agree with Phil Redmond's original post on this thread that mma hands are usually sloppy...with some notable exceptions like Fedor, Machida, Liddell, Cro Cop, etc.
But an underlying issue is the fact that what a pro boxer might have to say about the lack of skills in mma striking has to be taken with several (and one particular) grain of salt:
there is no kicking, clinching, striking in the clinch, knees, elbows, and takedowns allowed in boxing.
And it's especially the takedowns that require major adjustments when using striking hands (ie.- boxing, wing chun, whatever...) in an mma setting.
The whole striking game changes when clinch fighting and especially takedowns are allowed.
And boxing has to take this into account - regardless of how good the boxing skills.
In an alley....how much stick-and-move, use the jab and back away Ali-type boxing would really work? Incredible "boxer"...Muhammad Ali was (for example)....but he even remarked once that if he had to fght Chuck Wepner in an alley - he'd bring his blade!