Isn't this the same as not using Z elevation and using parallax instead?
Yeah kind of, in a primitive way. I could use dozens/hundreds of layers with different parallax settings, or I could just have 1 layer and change the Z elevation of an object.
I love setting the Z, but my graphics are all hand drawn to fit certain distances and I'd imagine pixel art users who want to keep the graphics consistent would feel similar.
It would allow more nuanced detail in parallaxing scenes, as I can simply and efficiently just adjust the Z depth per object, rather than getting lost in a complex layer system.
For the times when I do want something to drift from the background to foreground it would be much smoother than transitioning between the parallax layers too!