Kinda late to the party. My 'very original' thoughts:
6th FE rep seems extremely unnecessary, so I can understand the huge initial backlash (despite Roy being similar in Melee) since Corrin followed Cloud's announcement, which seemed to open up the floodgates for possible Smash candidates. I guess personally what's jarring is why FE gets so much spotlight when arguably Star Fox Zero and Xenoblade Chronicles X could use some promotion. I was thinking Corrin would've been saved for the inevitable Smash 5 alongside Splatoon, though seeing this will likely be Sakurai's last time as director and, let's face it, anime swordfighters sell (if Cloud and western demand for Isaac are any indication), I can see why Corrin would've been considered the most viable as DLC. That being said, Corrin, being the most controversial pick, is easily the target of backlash when x fanfavorite got shafted in Corrin's favor. Nonetheless, the whole dragon transformation undeniably looks pretty cool. (on that note, technically Roy is 'canonically' part Manakete, and Robin is Grima...)
I don't really have any strong opinions on Bayonetta. Looks cool, never played her games, and I personally am not in the belief that a more interesting/realizable character could've been in her spot anyways. If it wasn't obvious by now, Sakurai/Nintendo has a clear preference for Japanese characters. I really don't think Banjo & Kazooie or Shovel Knight stood a chance, let alone Golden Sun or *laughs* Donkey Kong Country/Metroid Prime.
Actually, I guess what's most surprising is how easy in theory it would've been to simply port Wolf, yet they still opted not to.