If, for some reason, they can't get the rendering priority right, another option would be to let us target & use skills on party/alliance members through the party/alliance list regardless of the visibility of their 3D model.

They had basically the same problem with XI for the longest time. You couldn't target or use skills on someone if their model wasn't visible. And player models went invisible a lot with gear swap macros for practically every skill being the norm. Your casts on other players would constantly fail or get flipped to someone else. Took them a few years, but eventually they made it possible to target & cast on someone whether they were visible or not.