I’m not sure I’ve ever given it much thought. It’s an editor that could certainly use some love (e.g. either you should be able to scale X and Y independently or it should be a single property), but it’s an area of the software that’s hopefully only used by relatively expert users, and it’s well documented.
Granted, now that there are more SMuFL fonts knocking around more people are more likely to go in and tweak things that don’t work for them, but that’s only happened in the last couple of years (since Finale embraced SMuFL, perhaps?) and I don’t think this dialog has had an overhaul that recently.
I’m not sure that your suggestion, of two separate sections - one for the currently selected object and another for new objects - would be any less confusing, though.
When editing objects on the page, the note value and articulation of a selected note are shown in the left panel and, if you select a non-note object, relevant stuff is highlighted in the right panel. With that in mind, maybe a more consistent approach would be to make it possible for nothing to be selected in the centre of the Edit Music Symbol dialog. That way, when an existing glyph/text object/image was selected, the right side could show the existing attributes of the object, and to replace it - similar to replacing a double barline on the score with a start repeat barline from the right panel - and when nothing is selected in the centre, additional glyphs/text objects/images can be added from the right panel (like clicking and dropping from the Write mode panels).
I have no idea what this would entail, who would do it, what they’re tied up with for the next six months, and I’m sure they could come up with something better given time and priority.