I feel like these sorts of arguments are conflating "relevancy" within the games and series the characters appear in and relevancy to present-day gaming at large. In the latter sense, Geno is about as relevant as K Rool because it's unlikely that either are going to appear again in any upcoming games (short of Nintendo deciding to revive the Kremlings...which I'd still say is more likely to happen than SMRPG getting some sort of sequel). But if you're trying to imply that Geno means as much to the Mario series (or at this point, even the subseries of "Mario RPGs") than K Rool means to DK, well...that's just flat out incorrect.
I thought Geno was fine enough as a character in SMRPG back when it first came out, cool but unspectacular. The immense and feverish amount of push for him in Smash specifically really boggles my mind at this point, though. You can love the character and hope for a miracle I guess, but at least be willing to recognize that the odds are absolutely not in your favor for something like that happening. It would be like me constantly pining for Mike Jones from Startropics to be a DLC fighter, yeah I technically could drive that train if I wanted to, and find ways to explain away everybody pointing out why it would be unlikely under the guise of "rules don't matter," but I can recognize in my heart that it's a losing battle and be happy for what is being added while also considering other, more logically-likely options to put support behind.