Something that I felt worked quite good in most games with a lot of skills are ring menues (Examples: Magika, Witcher 2, Secret of Mana.)
I made a drawing to elaborate:
You activate the ringmenu with one button and can then navigate in a 360° manner through all of your skills. It is fast and efficient and that's what counts if you have to use a lot of skills very often. Depending on screensize, the ring menu could be permanently shown at the bottom right/left side of the screen. One could then see which skills are on cooldown and it would effectively replace the hotbar.
A variation of the ringmenu:
One concern over the normal ring menu might be that joysticks might not be sensitive enough to navigate through the ring menu when there are, say, 20+ Skills. It might also get confusing. One solution would be to create artificial clusters/skill categories within the ring menu. Those Clusters/skill categories could then be selected and would contain 6-8 skills that have been assigned to that category. While selecting skills would take one more step, it would "clean up" the menu and give players the chance to create a better overview over their skills.
In both concepts, players should be allowed to freely move skills around to whereever they like (move to another category or move to another place within the ring menu)
You're welcome darkgod <3