Nobody will complain if Kitana or Mileena come back from MKX let's be honest. The target seems to be Sonya because they dont like her personality and find bratty Cassie more entertaining. Even though she's always been popular and is considered A-tier by NRS, people are "shocked" that she's back even though out of all the females she's been in the most games along with Kitana. Makes zero sense for her return to be shocking. Not to mention the impact she's had on a lot of people who grew up with MK, look and Ronda for an example.
Honestly, as much as I love Kitana and Mileena, I wouldn't mind either of them to take a back seat from the main roster in MK11 and then maybe be DLC instead.
Kitana in MKX was another example of "she's just there to be there", while Mileena was a prominent character in the story. Now Mileena is dead, and though that means little in the world of Mortal Kombat, ESPECIALLY now that the story is going to mess with timelines/time-travel and such, I feel Mileena staying out of the main roster and being DLC instead would be alright to do.
I'm not shocked to see Sonya back, not one bit. I would just rather Cassie was on the main roster, and then maybe Sonya could be a skin or DLC as well. As I've said before, I feel like that with most of the legacy characters, tbh. But seeing Sonya is now on the roster, I hope Cassie will be a skin for her instead, just so they won't take up the roster space.
I repeat myself here, but one of the main things that people complained about in MKX was the roster was just... dull. A lot of fan favourites were omitted from it, so I would just have preferred to see MK11 have some of those back!