By holding down R1, you can bring up any of 8 layouts (even empty ones) by pressing a corresponding direction or face button. As a CNJ, I have my heals and items on one layout, attacks and crossclass skills on another, class switching spread over two layouts, and stuff like mounting, teleport, and random stuff on another. I still have a few layouts that are completely empty still, too.

It seems clunky at first, I'll agree. But after you stop pressing R1 constantly to cycle through them, accidentally skipping the right layout and cycling through them all again .......... and just remember R1 + (relevant button) = specific 16-slot layout, you have essentially 128 hotbar slots accessible within two button presses on a gamepad. It just takes some micromanagement and practice using it effectively.