The good: OP admits they need to practice, they'll hopefully use their frustration to grow, and the guy giving advice was willing to give a whole rotation.
The bad: OP should have practiced their AOE and single target rotations separately since they knew it was a thing before hopping into grouped content, and opening advice with "Let me school you" Is pretty rude and I can totally understand why it would get to someone.
In the end, I think everyone should practice before they hop into grouped content, it helps a ton, If you don't then be prepared for advice or criticism.
I also feel advice should be given kindly and respectfully, if you can't do that don't complain about people getting defensive or being unreceptive to it because you're a part of the problem to.