I think it's clear that in the current metagame Diddy Kong is the best character and that a clear counter does not exist yet. Saying something like "he beats everyone at least 55-45" is really pre-mature though; a lot of Diddy's match-ups have yet to have time to really develop. I've certainly heard it suggested Mii Brawler does even or better and from what I've seen could believe it, but since Mii Brawler is extremely poorly explored (small Mii Brawler has barely even seen play anywhere as of now!), who knows? Even Miis aside, I have lots of theory fighter reasons to believe Peach and Jigglypuff should do pretty okay here, but these MUs just haven't been fleshed out yet as those two characters haven't been very popular in the early metagame. Even someone like Luigi who has been popular and explored has angles that are just now developing; there's a lot of reason to believe Ice Balls really help Luigi here, but how fully fleshed out is that aspect of Luigi's game since so many regions are just starting to allow customs? If we go full custom with what no one has touched yet, how well does Volatile Breathing used correctly allow Wii Fit Trainer to escape Diddy's throw combos that seem to be his core defining strength, and what does that mean for the match-up?
To extend the Brawl MK analogy, let's think about where MK was at this point in Brawl's metagame, just shy of 6 months in. MK was just starting to assert himself as the best character, and we still had a lot of avenues along which people suspected he might lose or otherwise be disadvantaged. It turned out that absolutely none of those panned out, but if they had, everything would have been different. It was more like a year into Brawl's lifespan that MK was a much more clear problem, and conveniently for this game, about a year in will be the point at which we'll be able to be pretty sure if a balance patch is ever going to happen. For now there's just too much in this game we really don't understand, honestly a lot more than we didn't understand at this point in Brawl since 6 months into Brawl we had already concluded half of a 39 character cast pretty much sucked and we had nothing like customs to contend with. In this game, we can write off maybe 10 characters at the most out of a 52 character roster (one of which isn't even possible to select yet!) and every character has 81 versions we have to think about...
In terms of the cultural effects, there reached a point where the mains of a majority of characters were convinced dropping their main for MK was the smart, necessary thing to do which was also about the point that over half of the community played MK as at least a secondary if not an outright main. Right now Diddy is a fairly popular character with many Diddy mains seeing success; relatively few players are feeling the need to join the Diddy bandwagon, and it certainly does not seem to be the case that a non-Diddy main can quickly pick him up and improve their tournament performance right now. If that changes, we'll talk, but until that's the situation, I think ban talk only hurts us.