My only and biggest pain point with Git is that it requires a lot of manual merging even in a small project. You have several branches that are several weeks/months old and they touch the same set of files. Eventually, when they'll be approved for merging, you'll have to manually resolve lots of conflicts in all of them, and do that repeatedly. rerere is supposed to at least save you from repeating repeating same merges in every branch you rebase, but in my experience it never helps.
Unfortunately, as far as I understand, jj won't help with issue of unnecessary manual merges either.
Merges / conflict resolution in jj generally work much better than in git.
When rebasing a big branch in git with conflicts, you usually end up having to manually resolve conflicts in multiple commits in a row - in jj you just have to resolve the conflict in the first conflicted change, and it usually adapts subsequent changes automatically.
Overall, rebasing branches with conflicts used to be a chore for me with git, and is now mostly a nothing-burger. Of course, I don't know the exact details of your scenario, so I'm not sure if it'd help, but I'd say it's worth trying, esp. if it's a common pain-point for you.
Is this the case even with rerere in git?
My anecdotal experience is that I indirectly need/benefit from rerere much less often because I'm not usually resolving the same specific conflict more than once. I fix it the one time and then jj is rebasing a whole lineage for me, starting from the early commits, not from the single-branch leaves. That way I don't get "I rebased one branch and fixed this one already, but now I have to do it again for a second branch that shared the same conflicted commit as the first."
By contrast, git rebase --update-refs does not handle sibling branches but detaches them instead, and git replay hasn't had much TLC for UX yet. Plus, the last time I tried replay it was still obliterating commit signatures.
This doesn't seem related to git or jj. If you have a conflict, you have a conflict. It's a social issue, not a software one. No software can resolve all code conflicts without people making final decisions. You can help the situation by automatically pinging people to refresh their old branches though.