People have different workflows, but mine is frequently, skim the documentation, make a prototype, refine code a bit, add tests, move stuff around, break stuff, rework code, study documentation, refactor a bit more, and then at that point I have enough understanding of the problem to go in at yank out 80% of my code and do it right.

If Copilot gives me working code in the prototype stage, good enough that I can just move on to the next thing, my understanding is never going to be good enough that I can go in and structure everything correctly. It will effectively allow me to skip 90% of my workflow, but pay the price. That's not to say that Copilot can't be extremely helpful during the final steps of development.

If those findings are correct, I can't say that I'm surprised. Bad code is written by poor understanding and Copilot can't have any understanding beyond what you provide it. It may write better code than the average programmer, but the result is no better than the input given. People are extremely focused on "prompt engineering", so why act surprised when a poor "prompt" in VScode yields a poor result?