If you squash merge PRs, this is equivalent to merging master back into your feature branch before merging to master.
I do that a lot to avoid commits mutating mid-review, so you avoid having to force push over reviewed commits (which is a sin)
I do that a lot to avoid commits mutating mid-review, so you avoid having to force push over reviewed commits (which is a sin)
The PR reviewer isn't the only person who will ever review your code, you know.
If you police atomic feature branch PRs instead of atomic feature branch commits, though, things actually work out OK.
(By the way, the even more compelling next step to your argument is: pull requests aren't artifacts! I've worked on projects that have emigrated from GitHub, and was left with just the commit log)