What if reducing the amount of server load due to user input solves the server side issues? Just sayin'.
Yes, instead of properly fixing the server load issues they would rather take a gameplay function out of the game and hope that it fixes everything. I'm sure everyone will agree..

Taking a single attack out of the players hands ... isn't lessening the combat.
Interesting logic.

It's streamlining the combat so the player can focus on the meat and potatoes in the heat of combat instead of the tedious chore of coming back to you #1 key.
What "heat of combat"? Is the gameplay so complex and fast-paced right now that you can't perform to your fullest? I don't believe you.

There is no "tedious chore" for keyboard players, and that problem (with the action bar) is easy to fix for gamepad users as well.

Yes, why not make a slight alteration to the existing controls to fix the problem instead of making huge changes that accomplish pretty much the same thing (or even make the game worse)? Why not indeed! That's the topic of this thread.