You do realize a bunch of people got their start during the Smash 4 days on this forum and with Smash speculation period, and thus usually have a pretty good memory as to what was happening back then because it really wasn't that long ago, right? The easiest way to look at things is just look at where people were disappointed with Smash 3DS' ESRB leak, and those were overwhelmingly Mewtwo, Ridley, and King K. Rool being absolutely absent. The best I can say to your point is that there was a general sentiment of no new DK content being a bad thing and the DK fandom was more split between Dixie and King K. Rool (though Dixie Kong was often, and to some degree still is, thought of as the compromise candidate if people couldn't get King K. Rool and the two camps largely overlapped with heavy support). People had been talking about DK content in Smash 4 for months because they wanted new stuff and DKC Returns had just returned the series to mainstream attention and people hadn't seen much of it (they would leave very disappointed from that game unfortunately). King K. Rool gained steady momentum from the point that Diddy Kong was announced to his eventual reveal in August 2018, with the only waning period being
after he got hit with the Mii Costume in Smash 4, which was largely created in response to the early ballot presence King K. Rool had.
That costume released in July 2015 and had to have been in development at least a month before hand it's safe to assume, so I think that's actually quite indicative of his popularity being before the ballot had actually really started. But more importantly, if you go back to the mid-2014 period of Smash speculation and check the K. Rool thread, you'll see pages filled with this video:
This video was what the K. Rool thread use to post every time we got a new member to the thread. It was the standard introduction for new supporters to King K. Rool and he was absolutely started to dominate discourse as Ridley's discourse had either become too toxic or people knew he was disconfirmed at that point (thus the entire shadow debacle that largely contributed to Ridley being a miserable topic of conversation post April 2014). K. Rool was already gaining momentum rapidly well before that October 2014 Direct, and even then, it was a sour time in the community with a lot of uncertainty to how Nintendo was going to handle post launch content and if they would really listen to the "core fans" at all. I would argue that basically no fan base was really gaining momentum between Smash for Wii U's release and the April 2015 Direct that confirmed additional DLC, or at least not in particularly meaningful ways as fans struggled with the awkward post release period of that game. The only real thing I saw from people in that period was more of anger and frustration with the lack of new DK and Metroid content, and I wouldn't really call those reactions as much of a foundation for an explosion in popularity. People had been expecting that content throughout the hype cycle leading up to Smash 4's release, and it largely wasn't there upon release, so the momentum had been there for quite some time. King K. Rool and Ridley absolutely we're considered dual titans of speculation by mid-2014 with Mewtwo always being present as well (though anxiety and anticipation was somewhat lessened for him because he wasn't carrying the weight of a beloved series on him like Ridley and King K. Rool did for Metroid and Donkey Kong respectively).
Banjo & Kazooie got more support instantly because of Phil Spencer's Tweet and is largely the only instance I've ever seen in Smash history of a character's popularity popping up that aggressively overnight. Geno's a weird one because during Smash 4's era, his support had largely cratered and he was left with a comparatively small support base as people didn't think we were getting Square Enix to the table ever, and well, he was Geno, so he was always a tough sell. He only revived more seriously once we saw Cloud and specifically his Mii Costume showed people he hadn't been completely forgotten and Sakurai even backed him up as option. He didn't really hit the peak of his popularity until after Ultimate had been revealed, and his strongest stretch outside of the Brawl era came post King K. Rool when it seemed like the planets were aligning for his inclusion (and most fan favorites were in a similar state that hadn't been shown as ATs at that point). And I'd argue that was the biggest Geno ever really got though his Brawl showing was certainly somewhat impressive too.
