I personally don't believe Cloud was to do with the ballot. I believe either Sakurai wanted him in, or Square Enix struck a deal (I mean the Direct that revealed Cloud had like, 4 or 5 Nintendo exclusive Square Enix games announced or shown off with new details in it).
A lot of people go on about how Cloud means "anyone is possible" and I say this in jest sometimes too, but in actuality, while Cloud was unexpected, he wasn't unprecedented. He may not have been on Nintendo all that much (and all of his appearances are effectively cameos), but Square Enix have a storied history with Nintendo, release plenty of games on Nintendo, and Cloud himself is THE JRPG character, just like how Mario is THE platforming character, Ryu is THE fighting game character, Pac-Man is THE video game character, etc. Considering Sakurai's track record of putting in third party characters that are truly icons, he honestly had every right to be more seriously considered. Kinda like how Rosalina was cast aside as "unlikely" by the speculation community despite her proven popularity, relevance to core Mario, and all of that. People mostly cast her aside because "lol she'd be a Peach clone".
Ignoring whether or not the ballot is a thing, Ridley is a special case. He is a popular choice (albeit in part for the wrong reasons), and Sakurai acknowledged this and outright said he has attempted to put Ridley in IIRC (or at least conceptualised him, I don't exactly remember). But he hasn't been included due to the fact Sakurai doesn't see any feasible way to put him in as a fighter from a technical standpoint, while also keeping the character's defining traits in tact.
As for K. Rool, his Mii costume means nothing. Plenty of characters have Mii costumes now. Inklings have Mii costumes, and even a trophy, and people still think they can get in. I don't see what makes K. Rool different here.