Earlier quoted context omitted.
FTP is neither sophisticated nor a network file system. Frankly I'd take Dropbox over FTP any day of the week - FTP needs to die. Thankfully your options are not limited to either Dropbox or FTP. Thus people who want simplicity can have Dropbox (or similar) and people who want control can have sshfs or any number of other tools out there that require some assembly but also don't suffer from the numerous problems that…
I’m not talking about FTP, which isn’t a network file system. I’m talking about NFS, AFS, and sucessors in that line of development. E.g. https://www.slideshare.net/mobile/snehcp/coda-file-system . I’m literally talking about the theory of the paper by Richard Gabriel ( https://www.dreamsongs.com/RiseOfWorseIsBetter.html ) which is that worse solutions often win because it takes too much time to bring a good solution…
NFS and AFS (from what limited I know of it) are more designed for local networks thus to leverage NFS over a WAN you'd then need to tunnel your connection (eg via SSH or VPN). So while there is obviously overlap between them and Dropbox I wouldn't really say the two are all that comparable.
However to answer your point, I don't think anyone would disagree with the specific part of your point regarding how simplicity is often better than something arguably more powerful. However just because something is simple it doesn't mean it isn't also good. "Good" is just a question of whether it meets requirements. If your requirement is that it can be installed and operated by layman then Dropbox is a far better solution than any other the other proposals you've mentioned.