okay then, link me to where this was said and where Ridley was mentioned with that quote.
But it shouldn't be a big shock if a cut character didn't return. It should be a surprise if they did. So Mewtwo not being back isn't a surprise to me.
and i'm pretty sure they probably originally had Dr. Mario (and Dark Pit/Lucina) as an alt costume instead but since his attacks had different properties, they couldn't do that. Which would explain his "return". Its definitely not an intentional return.
Mewtwo is an original character and therefore harder to implement. Therefore, i'm not shocked he didn't come back instead of Dr. Mario
Duck Hunt Dog is an iconic retro game character. The retro characters like Megaman/IceClimbers/LittleMac/Pacman/etc. don't have to be relevant unlike K Rool who isn't even the main protagonist of his series, Bowser Jr (like Rosalina) has been in recent nintendo games at least unlike K. Rool, and R.O.B. is a weird footnote in nintendo history (aka his relevency doesn't matter either).
and just because a character is "popular" and "requested" doesn't mean they'll get in