Also I didn't get to address this earlier, but why are we specifically replacing the female characters to "make room" for villains? As if female characters constitute a special category with a specific quota, comparable to the "villains" category, and they're taking up each other's slots? I feel like Toph, April, Sandy, Helga, Oblina, Korra, and even Lucy are in the game because they're Nick icons, not because they're female characters filling a quota. I mean they're definitely not minor characters, Oblina and Korra are protagonists of their own shows, and there are other female Nick protagonists who didn't even get into the game, like Jenny, Ginger, and Eliza. Or well-known side characters like Sam and Gaz. I also don't feel like they directly "compete" with the villains, because many of the iconic Nick villains I can think of are female characters, like Vicky, Angelica (if she counts), Azula, Kuvira, Tak, etc.
I'm sure there will be villains in the DLC or the sequel (which is practically assured considering how much more money this will make than what was "expected"), but there shouldn't be inter-roster competition for slots where the male heroes are assured to get in and everyone else has to fight for scraps. That's why I actually kind of like that Helga got in over Arnold etc, it keeps things varied and fresh.