We can speculate that it isn't true, but we haven't seen the actual results. I wouldn't be surprised at all if Isabelle won over K.rool, for example. The only character we know comes from the ballot is Bayo. The likes of Isabelle, Ridley, Waluigi, Toad, and/or veterans could've easily won over K.rool.
While i agree with your observations , and certainly agree that people were sleeping in isabelle popularity, big time, I think you are underselling K.Rool..
Normally K.rool wouldn't be too different than Isaac or Geno... but K.rool by most tallies of sites that concentrate the hardcore smash community K.rool in general did stand out usually by a wide gap.
What does this means? it means that even if hardcore fans could have divided opinions regarding super popular picks like Geno or Isaac, or another Zelda Rep, they usually agreed into K.rool...
And there there was Youtube where every famous youtuber and their dogs (and cats) started making videos regarding top ten characters in smash... i do think that the prevalence of that videos managed to actually influence the non hardcore fanbase (at least regarding k rool)
Just as an example i was talking the past week with a friend who doesn't own a single nintendo system and barely have played nintendo games (yet he always have a certain degree of interest to play smash) to the point hat he didn't even knew that smash ultimate was a thing. but he managed to remember that a character was announced (he likely though that it was dlc for the previous game) at which point i asked if he remembered who it was... was the dragon? (obviously he didin't knew jack about ridley) the barbarian? the croc? and yeah, he managed to recognize that the croc from DK series was the one announced.
Youtube is kinda a powerful tool this days. and is more likely that infulenced lots of younger players that likely won't know who the hell K.rool was otherwise. While thsi may be true also for geno and banjo kazooie, i don't think it managed to get to teh point of K.rool, which actually made posible for people taht didn't grew up witha nes to recognize him...
So yeah i do think that K rool did very well on the ballot (along Isabelle, Inklings, and the cut veterans) so it was clear to me that Krool was in. and if you ask me, yeah, certainly this game seems to be representing the ballot wonderfully, even if the data recopiled on the smash hardcore sites may have discrepancies...
BTW: I'm not even a K.rool supporter DX