But we're talking about picking a thing to replace FTP for the use-cases people were already using FTP for. It doesn't matter if it doesn't do something FTP already doesn't do, because presumably you were already not relying on that thing getting done.
FTP is used to exchange files, a task that HTTP/HTTPS and/or email and/or IM and/or XMPP and/or Skype and/or Slack and/or a hundred other services can do just as well if not better.
...But it does work on iOS. It's just not built in. For example, Transmit for iOS supports FTP, and includes a document provider extension so you can directly access files on FTP servers from any app that uses the standard document picker.
The post I replied to implies that iOS is (somehow) "artificially limited" to be unable to access FTP - or at least I interpreted it that way.
FWIW, I'm not convinced that "web-based" is a better alternative for read/write file access, assuming you mean file manager webapps. No OS can integrate those into the native file picker, so you can't avoid the inefficiency of manually uploading files after changing them. WebDAV works pretty well though, if that counts...
It's just needlessly exclusionary. One of the greatest things about "the web" is it's pretty accessible by anyone with a browser that's at least semi-mostly-standards-compliant.
Not working on iOS is like saying "Oh, this road doesn't work with German made cars. That's not a big deal, is it?"