I can happily say that this issue has been resolved! Using Xcode 27.2 beta 2 (27B5028f) and the GUI 'Delete' button successfully removed the orphaned runtimes and they have not reappeared! I will note, if you use Time Machine, ensure you backup AFTER you delete the runtimes. Despite performing a backup yesterday, I had to perform another one to see my storage savings (~150GB!).

I have filed a bug report FB24870526 for this issue as well. There seemed to be no resolution to this bug in this forum besides disabling SIP (which I do not want to do.) On macOS 27.0 (26A428) with this issue occurring on Xcode 27.1 beta (27A9269), Xcode 27.0 (27A266a) and Xcode 27.2 beta (27B5019j). I was able to verify that even after a successful deletion of a runtime via the Xcode GUI, that "xcrun simctl runtime scan-and-mount" will repopulate the now orphaned runtimes. I assume that Xcode itself occasionally runs this command which is why the runtimes will eventually repopulate in the list. I was also able to verify that despite xcrun simctl runtime delete [ID] succeeding and xcrun simctl runtime list showcasing the given IDs status as "Deleting" before being removed from the list when rerunning the command a moment later, that the size on disk du -sh does not change nor does the files listed under ls -alF.