Have you seen villager? If anything, they took out items from him. An axe is part of your inventory in every game. Olimar leads a team of minions with elemental specialties. Duck hunt dog was a stretch, but it's like you're actually playing as the player, being directed by the dog, somewhat in a reverse Pokemon Trainer fashion, not to mention they wanted something to show off oldschool NES stuff. Either way, clearly, Sakurai disagrees with you whole-heartedly
Now let's look at Ridley. First and foremost, each character is scaled to fit, but is kept in scale with its respective franchise (with the notable exception of pikachu, who is about 1.5-2x the size it would be, relative to Charizard/Lucario/Greninja). With Ridley, they'd either have to make him tiny to fit with the fighters, or huge to fit with Samus. Let's assume they do the former, shall we? So, now, we have tiny li'l Ridley, which looks goofy next to Samus. What're his attacks? Oh, a fireball? Cool, cool, not nearly as impressive at this size though. What else? Another...fireball. Alright, and claws. He can slash stuff.. and shoot fireballs. And fly. Any other notable things that wouldn't make him a charizard clone? Oh, stage tilting! Cool, not happening as a move, but cool. All in all, there's really nothing that sets him apart, or gives him any versatility in game, not to mention there's really not enough to substantiate a full special move-set, let alone 3. tl;dr - While I honestly think Ridley is a cool character, and a nice boss in the Metroid series, I really, really don't see how he could fit in to this game. And this is coming from someone who was contemplating villager back before Brawl.