Lucina: Popular character that will sell TONS of amiibos.
Dr. Mario: FLUDDless Mario, a thing that everyone wanted.
Dark Pit: a CLONE (even if he could be a completely different character) and a rep of a series (lo. They are only 3 games, and 2 of them are 20 years old) that doesn't NEED (and deserve) more rep than Donkey Kong (milion seller) or as many as Kirby (one of the greatest Nintendo IP), but Sakuri-san had make one game, so let's add mor character from that series (which, 8 years ago, no one cared about).
Yes, Snake deserved to be in, and you know why? Because Konami is a better partner than Calcom in this day (maybe not on the Wii U, but they makes a lot of games for the 3DS, while Capcom, Ace Attorney aside, isn't makeing much), so Konami deserve a rep, and anyone can rappresent Konami as Snake. MGS had wrote an important part of the VideoGame Hystory, and if it is a big series, it's all thanks to the NES port of Metal Gear. They aren't putting MGS games on Nintendo console because all they have made recently (Twin Snakes and MGS3D) were waste of money. And MGS4 being a PS3 exlusive had stopped Snake to be in Brawl? NOPE!