So much this, everyone always gushes over Azshara like she is some god, but she quite literally planted herself (And her empire) on the strongest font of magical power the world had ever seen and horded the magic for her self (and her collection of sycophants), once she lost it she couldn't even hold a shield up around a small portion of her city for more then a few seconds...
As for N'Zoth and his power up, do people really think he gave her more power then the well? At that point She wasn't even his best plan... he dropped most of his forces with Deathwings arrival (Her people are even used as an auxiliary force for him), No way is she given any more power then she needs to do her job...