Wow. Someone's a little facetious, I'd say.
The reason his fanbase got so "unpleasant", as you put it, was because of the past 2 games: Smash 4 (Wii U / 3DS). We didn't understand how we could get Dark Pit, Palutena, Bayonetta announced as the ballot winner then (I'm not one of the Bayo haters btw, she's a ton of fun!) or 7-8 FE reps (including one as DLC) before a series' main villain who should have been in since Brawl. Brawl especially because it was in 2008, also the year of Rool's last appearance. He perhaps should have been in Melee, even. It's not just a matter of K. Rool's fanbase anymore. How would people have reacted if Ganondorf or Bowser weren't in the roster? Iconic characters of their respective franchises? And instead we got characters like, I don't know, a 4th Link or, say, Pauline as ANOTHER Peach echo, respectively? We were complaining because we were getting fed up of biased and questionable choices over what we considered logical ones. But Smash 4 is basically excused because it was on 3DS, a system with smaller cartridge sizes, which ended up bogging down the Wii U version (I felt), which anyway was on a failing console that didn't have long to go before its death, even Smash didn't save the Wii U, and only a few years after, the Switch came along.
Ultimate, however, forgoes all that and is all about fanservice, as Ridley proved. K. Rool is not just a random flunky or scrappy nobody cared about. He's Donkey Kong's Bowser equivalent. Or used to be, anyway (thanks Nintendo...) . And K. Rool desperately needed this, both for his fans and for his future. K. Rool getting in is a big deal, not just for us, but also for K. Rool himself. I'm not saying you should like it, Osby. But maybe be thankful that the "******** fanbase" will basically shut up. lol.