If it turns out the junk truly disintegrates without any significant affect to the atmosphere then GP is saying that it’s not actually a problem and not actually “junk”. Space junk usually refers to stuff junking up things in the same way a rusted out sedan ruins a yard.
If the sedan disappeared it wouldn’t really be considered junk. If the sedan disappeared but left behind a puddle of poison the label would still apply.
Well it’s definitely junk or waste or garbage from the moment you are unable to use it or reclaim it. It so happens in the case of starlink satellites that we don’t have to burn that trash, it burns itself. If you want to say space junk is just the stuff stuck up there that’s fine, but there’s a short period of time where Starlink satellites are both in space and are junk.