They didn't provide an rsync example until later in the post, the comment about not supporting differential backups is in reference to using rsync itself, which is incorrect, because rsync does support differential backups.
I agree with you that not doing differential backups is a problem, I'm simply commenting that this is not a drawback of using rsync, it's an implementation problem on the user's part. It would be like somebody saying "I like my Rav4, it's just problematic because I don't go to the grocery store with it" and someone else saying "that's a big drawback, the grocery store has a lot of important items and you need to be able to go to it". While true, it's based on a faulty premise, because of course a Rav4 can go to the grocery store like any other car, it's a non-issue to begin with. OP just needs to fix their backup script to start doing differential backups.
The measure of whether a system of government is good or bad is not "how long it lasts".