Ignore in-reply-to patches from someone who is not the submitter
A common thing to do is to monitor our own patch series in patchwork. However if someone replies to your patch 1 (or 0, if it has a coverletter), that person becomes the submitter. I think the likelihood of having someone else replying to your patch series with a new version of a patch is very low.
Another problem is that when someone replies with a diff, it's usually a suggestion of something that could be done in addition, not as a complete replacement to that patch. In that case patchwork would create a new revision of that series and get lost since the patches don't apply anymore.
So, I think the best thing to do is to ignore patches that have the in-reply-to set and it's from someone different than the original submitter (by following the in-reply-to chain).