Same problem here about 6 months ago. One of my Powerheads went down while I was on vacation. Waited too long thinking corals would recover on their own since flow was restored. When it didn’t get better, I pulled all the really bad corals and put them in QT (Just about all the SPS). Lps wer generally fine.
Did 100% water change. Three acros ended up making it plus some Monti’s, Stylo’s and Birdsnest. Knock on wood I’m doing pretty good now. Fortunately I had some backups of the corals in my Frag tank, so I mainly lost time.
I have been reading alot like you and I think the thinking with the Doxy is to kill vibro bacteria. There is a Craig Bingham article out there somewhere. Also I think Mike Paletta had one. In a smaller, early caught scenario they have an Iodine dipping strategy too. The doxy is kind of a nuclear option.
Bingham suggested vibro is always present... but when an environmental change happens, infection can take over and run crazy coral to coral. I hope the doxy works.
If I ever see the weird “flesh off patchy” again in my tank I’m going to move much faster and pull any impacted coral, treat in QT with doxy, and do a 100% change on the display.