I really don't get why this attitude seems to be focused on Geno in particular. You don't see people going into the Lloyd Irving thread and saying "Lloyd would be a perfect fit for Smash. ...as a Mii Swordfighter costume, of course" and refusing to listen to any claims that don't support that point of view. Whenever Sora gets brought up as a character that someone wants, you don't see people asking why Sora should even be in Smash, nitpicking every single point that's brought up, and dismissing those points out of hand.
Bringing up the Cacodemon and Mallow Mii hats seems like a guaranteed way to get someone ranting about how the Cacomallow leak is fake, and anyone who believes it (or even thinks that it could possibly be real) is a "delusional moron", and yet other supposed leaks with even less supporting them (like the text leak from 4chan that claimed that a League of Legends character would be added to Smash) aren't met with nearly as much vitriol.
Maybe it's just that the character's popular enough to be seen as "competition" for other characters, given how limited DLC spots are, but I don't recall seeing nearly as much hate directed at Ridley, K. Rool, or even Banjo (who had at least two major competitors from the same company in the form of Steve and Master Chief, both of whom were quite popular, and seemed much less likely than those two despite his history on Nintendo consoles). This sort of attitude seems much more common in the Newcomer Speculation Thread, but I find it strange that it's being directed at Geno of all characters when people are starting to feel optimistic now that we know for sure that spirits can be upgraded.