Sir Ilpalazzo
Member
Sales have nothing to do with character selection, otherwise we would've never gotten Ice Climbers, Game & Watch, R.O.B., Captain Falcon, Lucas, etc.
Sales probably have a lot to do with character selection. The original F-Zero (and maybe X, I'm not sure) sold really well, and all of the others are special exceptions. Most of the characters in Smash Bros. aren't from unsuccessful or super-niche series.
I also don't see how Dedede is comparable to Medusa in any way. He's been in way more games than her, Kirby sells better than Kid Icarus, and he's more prominent in his series than she is in hers.