[M2Ys4U]

I think you're over-complicating some of these.

On point 1, I think legitimate interests covers this fairly well, but it would be arguable for sure.

On point 2, the right to erasure is not absolute so the fact that data are not purged from the database is not relevant. Legitimate interests also come in to play here.

On point 3a, the GDPR only mandates that data subjects are given access to personal data, so the WMF need not collate the information to send to them. Surfacing rev-deleted data might be more tricky, I suppose, Wikipedia has policies against posting personal data of other users and such edits will be oversighted where it's brought to admin attention (see WP:OUTING).

On point 3b, again the legal requirement is to give access to the data. Rectification and erasure is also straightforward (edit the page, ask for other edits to be revdeled/oversighted if the violate WP:BLP). Like you say, Article 85 offers wide protection here, too.