I love FFXIV, so this is not an attack on the game. However, the simple truth is that the default HUD/UI layout is... well, it's pretty rough. Depending on screen size, there are often TONS of overlapping elements, things positioned awkwardly, and let's be real; the Job gauges/bars are way too chunky and positioned RIGHT in the middle of your screen.
And how's this for super annoying; even when you convert them to use "simple job gauge", while they look SIMILAR to the HP and MP bars on your screen, they ARE NOT, in fact, IDENTICAL. They're a couple of pixels different. And even when moving them around with grid-based placement, they don't line up perfectly either, but are still a couple of pixels off-center.
Now yes, you CAN move things around or resize them (to an extent, anyways; but you can only SEE windows when they're actively displayed, and some things can't even be moved). And obviously, everyone will have their own personal "best layout".
But that's still no excuse not to try and improve things where possible.
Personally? I think what would go a LONG ways is simply to have options to quickly and easily scale the size of text and windows. A small laptop screen has different needs than a large living room TV. So maybe a couple of "presets".
Or to be able to have a more "minimalist" look while playing solo, whereas in group content, a more robust presentation.
Again, nothing dramatic needs changing, no need to reinvent the wheel here, just offer a default UI layout (or presets) that better showcase the game, with all the information you NEED visible,
Beyond that, personally I still think on the Character-sheet window, both the Job Crystal and the Off-hand slots should be moved to the top of the screen It would make things much more symmetrical.