From what I understand, Starfire was kinda a disappointment as well, not adding anything unique to the game. Enchantress, however, had a lot of different and interesting things added to her playstyle, making her rather unique from the rest. She is more creative than what she could have become, which is another projectile based spellcaster character.
Though the turtles have some moves that other characters have had in NRS games, like a dive kick, a cannon ball move, a multi-hitting weapon move etc, NRS have gone beyond than what they could have done - which is just making one character with a few assists, which is already in the game as seen with Harley and Cyborg - making sure that each turtle feels unique (yes, kinda like Triborg, but some steps further)... The difference is that Triborg was more a means to an end, to somehow put the cyborgs into MKX without having to give each of them a unique spot on the roster. The Variation system allowed that. Injustice 2 doesn't have a Variation system, yet for the turtles, NRS kinda put it into the game JUST for the turtles' sake... and they are freaking guest characters.