Beyond personal taste, the anime swordfighter reaction will often come down to "characters that have big become iconic within gaming culture outside their genre" tend to be more favorably received than those that have not. Sephiroth, Cloud, & Sora are significant enough that even those that have never played Square Enix games know who they are and why so they're so beloved. Byleth & Pyra/Mythra are well liked within their RPG circles (the latter especially so in Japan) but they're both too new and their fame still largely confined to their respective fandoms.
It's a phenomenon not limited to just JRPG's either. Why would a Kazuya or Terry Bogard get more muted reactions than a Ryu (or a hypothetical Scorpion from MK) despite the former franchise's massive popularity and the latter's long legacy? Because in much of the West, neither has quite penetrated popular culture in the same way Street Fighter or a Mortal Kombat have, and the immediate level of hype tends to reflect that.
I suspect a similar variation would happen with Crash vs Spyro in Smash. The latter is a very well-liked platformer series that's sold well, and the character could work extremely well in SSB... but they could never engender the same kind of hype as the former because Crash achieved a status above even that of platformer fans.