I wouldn't say he's the most deserving, people only really started wanting him when he appeared as an assist in Brawl, not counting the few really big Punch Out fans that wanted him before that obviously. The most deserving still haven't been shown, King K. Rool and Ridley have been getting the shaft for far longer.
Excuse me? I don't like Little Mac either bub, I'm pretty sure Jiggs just got a new buddy for my least used character, but I'm happy he got in, not for me, but for all the people that love Punch Out and wanted him to be in.
And you seem to have trouble differentiating roster space from development time. Mewtwo wasn't cut because Lucario was added, Mewtwo was planned to be in Brawl, but as you referenced, he was cut due to lack of development time. You know what that means? They ran out of time to make the game, not space. You want someone to blame for that? Sonic the Hedgehog. He delayed the game and took up the time needed for the cut characters that were planned. Does it look like they are rushing this game? They don't even have a release date besides "sometime this year." They have all the time they need to add characters, one character getting in will not stop another character from getting in. So dislike Mac all you want, but don't go around blatantly lying about him "wasting a slot."