If your github-fu was good, you could get the same result with copy-pasting. But then you would need to worry about licenses. It's very convenient that Copilot and the like don't disclose the licenses of their training data.
I'm curious, have you tried to use it on a week-long project? It's really not just copy pasting through GH, once you figure out the workflow. I consider myself an okayishly experienced dev (10+ years, if it even matters), and for things I've never touched (in my case, mobile/front end development), it's incredible how it sped me up.