It is, because you never know if there's a character that you'd end up liking far more than Geno, Ridley or K.rool in the long run.
It's far, far better if we get a healthy mix of both popular and unexpected. I'm not saying unexpected characters are better than popular picks, I'm saying that there needs to be both. Focusing exclusively on requests is what would make a stale roster. If we hadn't gotten Greninja and Zoroak made it in instead, the roster would've been outdated on arrival.
Also a question for Geno supporters, just curious. If Smash didn't exist, would you still care about him?
Zoroark isn't exactly a long-time fan favourite though, and didn't even end up being as popular as Greninja in the long run. Not at all comparable to characters like Ridley, K. Rool or Geno. Unexpected picks are nice but I'd much rather have a roster where it feels like everyone has earned their spot, newer characters can always get in the next game if their popularity is significant enough, like what happened with Inklings. Also, Smash's roster doesn't need to be modern and fresh to be good, so what if it's outdated as long as the characters are new to Smash? Melee's most modern characters were Roy and Pichu, with most other characters originating long before the Gamecube. Brawl was a little more modern, with Ike, Lucario, Lucas and (depending on what you consider modern) Olimar and Toon Link. Not once have I ever thought that those games didn't have enough newer characters. I'd actually say that Brawl probably had the best roster in the franchise up until now (aside from lacking Mewtwo lol)
Even old character's feel new in Smash, the idea of playing your favourite character in a cool fighting game doesn't feel any less good because that character is old. And older characters have had a longer time to establish large fanbases, meaning that feeling is spread out to more people. If new and fresh characters was an important factor, Smash 64 would've never gotten off the ground.
I'd like some unexpected characters, but if our roster is being limited to 8 unique newcomers, or maybe less, then I'd prefer full on fanservice 100%
Also, SMRPG gets rereleased all the time, meaning it's getting new fans all the time. Everyone I know who's played that game instantly loves Geno. Him, K. Rool and Ridley are also each enjoying renewed relevancy and exposure thanks to the release of the SNES classic. They're beloved characters not because having them in Smash is a funny meme, but because they genuinely make an impact on the people who've played those games.