Least wanted characters, eh? If you can't be a character I actually want in then you can at least either bring representation to a legacy that deserves it or be new and exciting. (subjectivity ahoy)
The legacy thing works for Ryu, Terry and Hero despite not caring for their franchises in the slightest; I respect them for it. It doesn't work for, say, Joker who is literally only repping P5. Doom Guy or Crash would easily meet the criteria despite not being the biggest fan of either. Legacy is not just "this character is old" either; I don't think Ice Climber or Duck Hunt are interesting additions because they've done nothing with the characters for yonks so their legacy is little more than a gravestone. Even Pit with his Brawl-only redesign before Uprising was a twinkle in Sakurai's eye had the interesting little factoid of being Metroid's forgotten sibling game and being reimagined as if it hadn't dropped off after the GameBoy. Little Mac punched his way out of the grave and didn't just bank on "remember that wireframe guy from the boxing game", etc.
The 'something new' is usually new IPs. It's really less of a check for new IPs than it is a big fat X for franchise repeats that don't bring anything new like the 8th FE character or generic Mario baddy. You'd honestly have to try to find worse additions than those two; Slippy Toad or Urban Champion or a Pacman ghost would honestly be preferable because they stand a better chance of standing out. No, I don't buy that having an interesting moveset alone justifies inclusion. Literally any character can have an interesting moveset and they can do so while also being interesting characters from interesting franchises who can interest people by virtue of being their introduction to said interesting franchise, rather than the Nth reminder that "oh yeah Fire Emblem still exists". I love Fire Emblem and there are characters from it I would've loved (past tense) to see in Smash but at this point I'd rather just see anything else get in to spread the love around.
So really as long as you're not another ****ing Fire Emblem character and your support content isn't actively being sabotaged by your parent company you're fine in my book. watch as FP5 can't even manage that, my god am I upset about this extra content for a child's toy pre-emptively