I'd argue it's kinda a myth, because I used to believe we could create a perfectly closed loop (you know, like the one the recycling symbol suggests) if only we could cleanly separate the materials (which in my imagination requires consumers to vigilantly separate the waste into dozens of different bins). I'm beginning to think I was wrong.

If 1kg of "recycled" plastics allow to reduce the production of 1kg of pristine plastics, it's already a big win, even if it's downcycling. No need to throw away the baby with the bathwater.