For what it's worth, the Flickr app now automatically backs up every picture; so do Picturelife & OneDrive. They all are backed by a storage array that is quite a bit economical when compared to Dropbox's current rates.
If yahoo shuts down Flickr tomorrow, it's users are screwed. If Dropbox shuts down tomorrow, all my pictures are on a handful of drives. Again, major difference in how it works.
Dropbox turned down buying Everpix last year, who had been an extremely promising photo management startup---because DB we're working on this. Most relevantly, the author of this article gives lip service in the first few paragraphs to the idea that design is how the system works, then reviews them based on the surface UI. He doesn't seem to look at the sync protocols of sync-focused apps!