Well, Scorpion's HKHKLKLK combo is different thank Human Smoke, but that isn't really an advantage. In MKT he has a front teleport, which can be useful for building up nice combos, but it pails in comparison to Human Smoke's pop up dial combos. Those are what make him the better version. Scorpion is kinda pointless in UMK3, but he is definitely more unique in MKT. And yeah, picking Scorpion can be more fun sometimes ^^.
I can see your point, yes there is a lot of characters better than scorpion, but this is a game. People play it for fun, why should no one ever use him, just because human smoke is better? I pick him just for fun all the time. It gets kind of boring when all you ever play is human smoke and kabal, just because they are the top characters. It's fun to learn how to effectively use ALL of the characters.