Some thoughts I've put together, especially regarding the Banner Leak (because no one seems to be talking about that around here):
Sakurai
I feel like there are two sides to the man: the master and the mischief maker. When the master is present, we get nothing but seriousness. This is the one that shares info about the depth and scope of the game, the mechanics, the little details that just blow our minds (Olimar's helmet, Sonic's stopping sound, Cappy popping up, Bayonetta's guns making different sounds, etc.). This is the man that makes us all worship him as a god of game design and direction.
But then there's the other guy. When he's present, he takes delight in trolling us at every turn. The Waluigi post during Sm4sh ("just because you try hard doesn't mean you'll make it in the game"), the ZSS "removal announcement" during a Sm4sh direct, and most recently King Dedede literally laughing at us during the K. Rool reveal. The dude likes to surprise and fake out his fans, and we like it too!
WWhy do I say this? Because sometimes the two get confused for one another, and it's fair to see why. Without hindsight, we'll never know for sure. When E3 happened, we all thought we were only getting 3-5 more characters after Ridley. We got 5 in one sitting in August. He said that the pace would be slowing down (which, in terms of reveal frequency, is true). But what better way to blow our socks off by having 1 or 2 directs that UNLOAD hype on us right before launch?
Incineroar/Vergeben
We all put a lot of stock in our boy, Vergeben. He's had a pretty consistent record and we all really liked having a "trusted source". When he said Ken, we all thought, "Sounds realistic." When he said a SE rep, we all thought, "Geno, Sora, DQ...ok. I could see that." But the reality is that I think most of us expected these two things. However, when he finally said Incineroar, two things happened: 1) hardly anybody was excited and, 2) everyone else started parroting the character in their "leaks". Sure, there were people saying it before, but Vergeben effectively killed all other Pokemon speculation with his comments.
Why did this happen? Vergeben has always only had one thing on his side: his word being verified. The reality is that he could be a really good guesser. I know that's unlikely, but there is still a possibility. He's very smart in how he posts, only saying one or two characters or details at a time. He doesn't go on blast like other "leakers", a strategy which, if just a lie, mitigates the chance of him getting caught.
But even if he does have sources, sources can be wrong. It's asinine to assume that a good track record means infallibility in the future, especially when it sounds like he is the middleman to the information.
So where am I going with this? Well it's very, very possible that Vergeben simply got Incineroar wrong. Had he never said Incineroar was in, I honestly don't know how many people would stand behind the character as much as they are.
The Ballot
Let's assume that when Sakurai was interviewed about King K. Rool, his comment about him preforming well on the ballot were from "Master Sakurai" and were 100% truthful statements. (My main justification for this is that I really can't see any reason for him to lie about this detail. It would literally do nothing for anyone if he did.) That being said, it's clear that the ballot is influential in the roster choices in this game, or has been for at least a few characters. Another poster (who I can't identify because I can't find his/her comment...sorry) made a great point. With the evidence we have from online ballots and polls, combined with what we've heard in Smash's social circles, I think it's fair to say that Daisy, Dark Samus, Chrom, and Richter were NOT ballot champions. Sure, there was popularity there, but nowhere close to characters like K. Rool. The Inklings were a shoe in (because of popularity, both from sales and fans), Simon is kind of classic (and was probably part of the "Snake again" deal), and Ridley was kind of a BIG deal. Outside of K. Rool and possibly Isabelle though, I don't see Sakurai pulling from the ballot for the other newcomers. And we know for sure that Ken and Incineroar were not frontrunners.
And Now The Banner Leak (Conclusion)
Tying this all together, this is why I am part of #TeamReal. (You can read the following statements as one, flowing, cohesive thought. I've "titled" each section with my previous subjects for guidance on why I've come to this conclusion.)
Sakurai - Sakurai wants us to be surprised and extremely happy about what could be his very last (for real this time) Smash game. This has no doubt been a massive undertaking. But for anybody that wants to be a winner - the best of the best - would understand, you either go big or go home. For him, that probably meant fulfilling every possible desire and dream he could in this "Ultimate" version of his "Special" baby.
Incineroar/Vergeben - Like the September 28th leak says (among the gratuitous profanity), Nintendo really wants to blow our socks off. So when it comes to who's in and who's not, we've looked to leaks until Nintendo tells us something. Most of them have been text leaks, and when it comes to evidence, it's got an "wrong until proven right" kind of thing going on: a leaker is has to be proven correct with official news. But I think we can all agree that, when it comes to leaks, video>image>text. So even though Vergeben has some credibility, and has been our most "trusted source", we have only gotten text leaks from him. Images and video leaks carry much more weight, so if something came out contrary to what a text leak says, then the image/video wins until discredited (which, interestingly enough, goes the other way when it comes to credibility: right until proven wrong). So I think Vergeben, as right as he has been, is up against a powerful foe with the banner leak.
As for ending off with Ken and Incineroar...yeah, no. I honestly think the former was just bad info that got circulated among those in the know anyway. Besides, this would be such a lame ending to a fantastic hype-cycle (possibly the most hyped up game in history, at least in recent memory for me). People have said "but what about ending with Olimar in Brawl" or "Shulk wasn't that cool for Sm4sh", and you've got a point. But the problem with this point is they aren't Ultimate. The game is called "Ultimate" for a reason. It's the final chapter, the end all, the climax.
Watch any movie series and you'll see this at play. Take the MCU, for example. Each individual film is great on its own and has its own exciting parts. Some are better than others. But they are all building up to something greater. And when the 4th Avengers finally hits theaters, we'll get to finally experience the climax, the "ultimate" Marvel movie. Or should we assume, using the same broken logic permeating pessimistic comments, that the final Avengers movie will just sizzle out at the end because some other films have done the same thing? Of course not! Disney and Marvel have made sure that this sicker ends with a bang. Why would Nintendo (the only company with IPs to rival Disney, IMO) not do the same?
The Ballot - And just like the Avengers, we want the most legendary characters the company can get their hands on to be at the party. And when it comes to heavy hitters, we're running low. But there are some with a lot of power still. The holy trinity of Geno, Isaac, and Banjo and Kazooie would break the Internet if revealed within 24 hours of each other, let alone the same direct. They are all very popular among the Smash community (as evidenced by polls and the most recent bracket done on reddit...I wish I had the link or user name to post for research purposes). I would imagine that in the official ballot, they placed pretty high. Why waste that good info and go awol choosing Incineroar or something less popular or obscure? That's not a smart business choice and is contrary to common sense.
As for the other characters, Chorus Kids are neat and extremely unique. Mach Rider is classic Sakurai giving us our WTF character. Shadow and Ken are no-brainer, popular-enough third-party echoes. This fleshes out the roster well and gives it a truly "ultimate" feel, representing gaming in the most diverse, legendary way.
Analyzing the banner roster leak, well let's see...it would definitely be a huge troll on Sakurai's part if it was true (but also make him the absolute master of gaming), it is an image leak with immense amounts of complexity which gives it a lot credibility, it doesn't disappoint with its incredible roster, and it has some of the most requested characters in the Smash community. It checks all of the right boxes. At this point, until something substantial comes out to prove it's a fake, or until the source comes clean, we get to claim it as gospel and bask in its hype-giving life.