@Dekar, everyone on the Diddy boards minus a select few believe that the MK knows how to use the bananas to a good, realistic extent, but not to some unsaid potential. You can't say, "MK can expirement with bananas, new things might be discovered, and then the matchup is much worse."
It's just a logical statement; Diddy plays with bananas every single game. MK only plays with bananas versus the Diddy matchup and on their own random time. Diddy uses bananas more, meaning that he should know much more of his possible followups and such with bananas.
At top levels of play, Diddy will logically have more banana knowledge. And even assuming that the MK has equal banana knowledge, the mere fact that Diddy can spawn bananas whenever he chooses means that he has the advantage. MK mains in that thread said that it wasn't that they didn't know how to use bananas, but Diddy kept them under his control so well.
No one really won that argument between Hanson and P1/AZ...
Also, a character having good matchups against other characters does not make them unviable. This would also mean that Snake, Falco, D3, heck basically EVERY SINGLE CHARACTER other than Captain Falcon makes another character unviable, and that logic is just silly.
Making a character unviable means that the character just can't be used competitively. The closest thing to this is D3s matchups against Donkey Kong, Mario, Luigi, Samus, and Bowser. D3 makes Donkey Kong unviable because he has an easy infinite on him, and a ridiculous match-up against DK. Anyone can simply CP D3 when they're losing to a DK, and congratulations, 99 times out of 100 they win a game of the set.
Does MK do this? Does MK have any completely **** matchups that are specific to him and him only? The answer is no.