That one YouTube guy who talks about Ridley basically plays up this "loudmouth ignorant gamer" persona to get attention on his channel, and it works. He pumps out videos with titles like "RIDLEY IS TOO BIG" and "STUPIDEST CHARACTER SUGGESTIONS," and, because he speaks in absolutes and swears semi-frequently, he's developed this cult of YouTube followers who consider his every word to be gospel. He also sticks in little comments like "If you ever see anyone supporting Ridley, show them this video to shut them up" for additional attention, so, naturally, Ridley fans don't like that very much.
As far as K. Rool's athleticism goes, I'd guess he'll either have decent speed or decent jumping, but not both. Even though being a massive target is crippling enough for most heavyweights, Sakurai can't seem to help heaping on additional weaknesses, sad to say.