GH Copilot is definitely far better than just a linter. I don't have examples to hand but one thing that's stood out to me is its use of context outside the changes in the diff. It'll pull in context that typically isn't visible in the PR itself, the sort of things that only someone experienced in the code base with good recall would connect the dots on (e.g. this doesn't conform to typical patterns, or a version of this is already encapsulated in reusable code, or there's an existing constant that could be used here instead of the hardcoded value you have).