If I import a FBX with multiple meshes in it, there should be easy way to turn them on and off on a model.
Not material id's, not selection sets, not geometry masks, no setting shader to opacity and painting over things you want to hide, none of this around-the-corner nonsense.
There should be a tree showing FBX file contents (meshes) and checkboxes to turn them visible or invisible (which should also make brushes ignore them!). Why isn't this a thing??? Or if it is, where is it hidden on this bloated UI?
It's evident that Painter already detects separated 3D elements, because you can fill by element. Just make a list of them!