BB folder and file type structure makes it relatively hard to back up just some files of given type. And some stuff like tars and zips could be arbitrary in size and importance.
Having said that, we offer the ability to exclude folders and filetypes if you have certain things you want to backup later.
(Not disagreeing with anything you're saying...just fyi.)
Gleb from Backblaze
Backups transfers are also a minor pain point - the error horse (on freshly installed BB on windows) and when, how and why it disappears and allows you to do the backup is still a mystery.
I guess that the BB cloud storage will solve some of the customization problems though - if you are power enough user you could write a custom strategy on top of the API.