ROB is the biggest camping piece of crap in the universe, as well as probably the worst character in smash history (sans late addition clones in Melee). He's generic, uninspired, and honestly just a campaholic. Honestly if a character was cut, I'd cut ROB. If you've ever been in a 10+ minute long 3 stock match and got timed out against ROB, you know the feels man. You know the feels.
Of course all that can be fixed, but from my viewpoint, I'd rather have back characters who are proven to be fun, balanced, and stand out as unique characters than those who thus far IMO haven't been fun (ROB), balanced (Meta Knight, Zelda on opposite ends), or stand out as unique characters (ROB).