Excuse me? But this has to be the most fucked-up thinking i have ever read. You basically turned BOTH characters around 180°. Azshara is the one who does things because she believes they are necessary. She allied herself with Sargeras because she visioned a perfect worl of beauty and saw that his powers were far greater than anything on Azeroth (which they were). She then allied with N'Zoth to continue her reign and still fight for this "perfect" world she envisioned. Azshara has NEVER - not a single fucking time! - ever done something evil just for the sake of it. Everything serves a plan. Always.
Now look at Sylvanas. She has freaked out and totally lost her shit PLENTY of times. She may have had some kind of plan (Spoiler alert: There was no plan) why the destruction of the Night Elves was somehow "good" for her...or the Horde..or frankly anybody on Azeroth (spoiler alert: It was not)...but then she burned down the tree simply because she had to spite a dying woman who had fought valiantly to the end to defend her home and race. It reminded her too much of her own death at the hands of Arthas...and she saw that Summermoon was not yet as broken as she was back then...which angered her. She burned down the tree to torment a woman who would have died anyway. That was the ONLY reason why she did it. There was no more to it. No grand plan. No greater cause, No hidden truth. THIS is the truth. She is simply evil and hates both life and hope because she does not have any for her own.
Now, as you said: That does not make her a bad character. But please don't try and soemhow twist her into anything else but a simple evil puppet-character. Especially compared to characters like Azshara that indeed DO have a greater cause for what they do and don't.
[Infraction]