This argument is a good one but it only covers the rise of Dropbox. We are now in a different era.
Dropbox's functionality is now table stakes and not something new. Windows by default has cloud sync, macOS does as well. We switched at our company from Dropbox to Google Drive Stream. Box is really focused on enterprise solutions -- lots of permissions, probably too much in my opinion but C-suite like that shit.
This quora answer is irrelevant in the current context. Dropbox needs to figure out how to stay in a commoditized market where their special sauce is being integrated into OSes and larger offerings (G-Suite.)
Maybe a return to simplicity is it? But we moved away from the simple solution because it wasn't sufficent for our needs. And others are just never adopting it in the first place because it is built into their OS or their app suite. Dropbox has a long-term relevancy problem here that they have not cracked.