You can specify a commit, yes, but how do you remember your set of unnamed commits? Once HEAD no longer points to a commit, it will not show up in `git log`.

I agree that Git could gain an operation log. I haven't thought much about it but it feels like it could be done in a backwards-compatible way. It sounds like a ton of work, though, especially if it's going to be a transition from having the current ref storage be the source of truth to making the operation log the source of truth.

Mostly, yes. It also covers changes to the working copy (because jj automatically snapshots changes in the working copy). It's also much easier to use, especially when many refs were updated together. But, to be fair, it's kind of hard to update many refs at once with Git in the first place (there's `git rebase --update-refs` but not much else?), so undoing multiple ref-updates is not as relevant there.