Copilot can use any model like Sol or Opus and is just a harness so not sure why people say this.

Personally it's because i used it when it was brand new and work paid for it and i had no idea what model it was using, my boss just turned it on for automatic PR summaries and code reviews and it was universally dogshit, and the auto complete in my IDE was awful as well.

Well it's much better now.

Well the PR summaries are still dogshit lol

Guessing this is the relevant part: "worst AI model I ever used"