You are overthinking this, this is wow.. a 12+ game that just gave us a reason why Sylvanas was evil all this time.. probably out of all option they had left.. this option had the most votes in the team. The difficult thing about this.. for me that it doesn'tt feel genuine at all and feels like a last resort or something, we know we ruined her, but this is what we can do, to slighty please both sides of the opinions. We were set to believe this was the real Sylvanas and just formed by tragic life experience..., nope all staged.
It gives them both a reason to explain her evil side( lol), but also give them an option for her to return in some way.
It's like high elves.. can't please one side.. lets destroy the meaning high elf and give it to both sides, you can't please everyone.