This is a great point! But there's an important tradeoff here about human engineering time versus the "learning in the open" benefits; a PR discarded privately consumes no human engineering time, a fact that the humans involved might appreciate. How do you balance that tradeoff? Is there such a thing as a diff that's "too bad" to iterate on with a human?
I do agree there is a balance here, and that the ideal point in the spectrum is likely in between the two product experiences that are currently being offered here. There are a lot of benefits to using PRs for the review and iteration - familiar diff UX, great comment/review feedback mechanisms, ability to run CI, visibility and auth tracked natively within GitHub, etc. But Draft PRs are also a little too visible by default in GitHub today, and there are times when you want a shareable PR link that isn't showing up by default on the Pull Requests list in GitHub for your repo. (I frankly want this even for human-authored Draft PRs, but its even more compelling for agent authored PRs).
We are looking into paths where we can support this more personal/private kind of PR, which would provide the foundation within GitHub to support the best of both worlds here.