I take it you're not a fan of Falco, Toon Link and Ganon?
I'm fine with Falco and Toon Link because they do actually fit a lot of my criteria. They fit the justificaitons for being their own characters and having movesets similar to another character (although making them feel as different as possible is a must (like Brawl Falco or Project M Toon Link)). Ganondorf has no reasoning at all for being a clone of Captain Falcon. When has he ever used something along the lines of Wizard Kick or Warlock Punch in an LoZ game?
To each their own, but I'm curious as to what the other criteria are? From your implications, Doc is fine otherwise, he just happens to be an alternate costume of Mario. Not being flippant and condescending, I'm genuinely curious as to what else you believe is important for a character's inclusion.
Well, mainly
-Justification for being a playable in some form
-Justification for them being their own character, rather than a costume of an existing character
-Justification for them having a moveset similar to another existing character
-Justification for their design or gameplay being based off of
x rather than
y
That's just the general stuff, though.
Devil's advocate: Doc represents an important, yet often overlooked, part of Ninendo's history, i.e. puzzle games and the Dr Mario sub-series in general. His moveset and physical attributes are distinct enough from Mario to warrant his inclusion, as they appeal to his particular fanbase and players who prefer the fighting style he possesses. He offers a lot of what Mario can't do and allows for more freedom of playing style and opportunities for distinct, creative moves that Mario does not have. He is a throwback to Melee and an appreciation of fans who prefer Mario in that game or, perhaps, just outright prefer Doc.
In a perfect world, Nintendo could just do like the Project M guys did, merging the positive gameplay aspects of both Mario and Doctor Mario and make Doctor Mario an alternate costume for Mario. However, as evidenced by a message of mine being flagged by moderators on Miiverse, Nintendo does not want to acknowledge Project M or any Brawl mods at all.
Come to think of it, we haven't seen any gameplay of Doctor Mario yet. Perhaps they made him feel less like a clone in this one. If that were the case, then i'd be fine with him.