How hard is it to press Alt+1/2/3?
If you are organised with all 3 of your hot bars and know your hot keys, there is no need for the extra screen clutter.
I have my stuff into 2 tabs already(ALT+1 Earth and Water for rest, ALT+2 Wind and Fire for crowded dungeons)
But opening windows or changing tabs gets annoying and losing time.
Some classes don't require so many key-bars because they have few skills (thats why i suggested for these key-bars to be visible if the player wants).