There are a lot of things that could be at the core of your problem, and I hope you reconsider.
1.) Clicking vs. Key Binding
2.) Mouse movement vs. Key Movement
3.) UI configuration. (It’s HUGE)
4.) Deeper and more detailed understanding of azerite traits and talents.
I could go on. But what I’m trying to say is, this might have nothing to do with your capacity to get better but rather a lack of knowing what the problem is. If you find yourself willing to try again, try to find someone or a group ingame to play with that is willing and able and happy to sit with you and work through finding exactly what the issues are that are preventing improvement. That’s all it is. I promise.