Nice visualisation. If you break out NIP-17 into "1-to-1 only" and "1-to-1 plus group" it gets even more fragmented.
Discussion
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Updated with new column 
nostr:npub1hyxredcavc6ruqgsf4wf4hmakpwnvefmzaspl7dja6a2sxlx0q3sxwtqnx do you have a concrete answer to
https://github.com/nostrability/nostrability/issues/169#issuecomment-2691307906
I think he replied to his own question, there are a few with 1-on-1 only in his reply.
But on his point that it's more work to remove groups than to add groups, I'd argue that NIP 17 groups are like fake groups, nobody can leave or join without breaking the group, so they should be removed for that reason instead, everything to MLS.