It is actually extremely funny that you think this is about keeping Threads data off of your instances, and not about keeping the awful content on your instances away from their users.

I'm sure it's fun to take this pretend victory-lap, but all you did is trivially break authorized fetch in a way that they will quickly fix, and they probably only implemented it because it's part of the ActivityPub standard.

At the end of the day, you'll have read-only access to Threads posts the same as any logged-out user, and they'll block your reach forever.