My biggest beef with controller gameplay is enemy targeting. I use a combination of tab-target (L1/R1) and face-target (X to select the enemy you're facing). It's pretty frustrating, but I've gotten used to it. The main issue for me is that the face targeting isn't sensitive enough, and tab targeting feels so random. If it just cleanly scrolled through enemies on my screen from left to right, ignoring depth, it would be a lot easier. We really need some QoL on this issue.

As for going back and forth between your target and the tank, THAT, I can help with. I use L3/R3 for this. I have L3 keybound to "Assist", which targets whatever your target is targeting. And R3 is my keybindable #98 macro, which instantly targets my focus target.

I can get to the MT (or whoever has aggro) by simply hitting R3, then L3. And I can always get back to the boss after scrolling down the party list to heal someone by just hitting R3.

Scrolling around the party list is definitely a bit slow, but I prefer that to misclicking with a mouse. And personally, I've never been able to play hotbar games with KB/M. It's beyond me how people manage it. I could do it if I had a pricey mouse with programmable buttons, but a PS4 remote is just so much more reliable.