I too have reservations about Copilot, but does the MIT license define a "substantial portion"? I doubt a snippet would fall under either "copies" or "substantial portions"
I doubt many licenses define that kind of terminology. That's left to precedents established by actual cases. My point was just that you're not free to use code from an MIT-licensed project without following the terms of the license. The other details get worked out when legal actions are taken.