This would be useful if combined with a warning that the alt text field is blank. Otherwise, it essentially does nothing to IMPROVE accessibility except to increase the number of blank alt text fields in websites curated by those who do not understand accessbility!

When used correctly, the alt text fallbacks were a timesaver for curators who had large sites. Now we'll be simply be copy-pasting the alt text from the title to the alt text field because we only need the one field to describe the image overall!

However, I do concur that having the caption text be the default alt text was confusing to the user, because you would end up with the same text in both the caption and alt text! Useless.

The superfluous field here is the title field; I'd prefer to see it removed in the long run.