I can totally agree to your assessment of the situation, but where is the perfect solution?
If there is no perfect solution, wouldn’t it be reasonable trying to get as close as possible instead of making no attempt at all because it doesn’t look pretty conceptually?
I’m very glad you asked both of those questions 
Apple Time Machine is the existence proof for dependable, easy-to-use consumer-grade backup software. It ticks all the boxes. Anything else aspiring to be consumer-grade backup software should study Time Machine inside and out before getting started.
Failing that, rsync is the standard solution for the technically proficient to produce a complete, correct, restorable backup of all data and metadata. The problem is that you need to build up quite a complicated recipe to get it right, especially if you have tricky partitions and odd data caches like Android. If you get it wrong, you have no backup. I can use rsync on a Linux server, but it’s too risky to roll my own solution for Fairphone. It takes someone with in-depth knowledge of that specific environment.
The wider point though: backup software is not an appropriate field for a “do your best and learn something new!” attitude. Like encryption software, a flawed implementation is worse than no implementation at all. Seatbelts don’t reduce injuries as much as they should, because the sense of security causes people to take more risks. Flawed backup software is like a cardboard seatbelt.
If you produce a consumer-targeted backup product that claims to make a backup but does not, in fact, make a backup, you’re doing more harm than good. You should stop, or at least slap “alpha software do not use” stickers all over it. Do not waste time attempting to build a product when you know you will never have the resources to do it properly. Save your time and energy for something that can make the world a better place.
In the Android world, all the oxygen in the room is sucked up by the two standard backup solutions: Google’s cloud, and “nothing”. Almost every Android user is happily using one of those, largely because almost no users of IT give any thought to backups in the first place. I have a lot of sympathy for people trying to do better. But it’s gonna take either a lot of deep strategic thinking or a big pile of cash to make something that’s better than nothing. Sorry.
My practical proposal for right now: all the solutions we have should change their names to something other than “backup”. “Migration assistant” maybe, based on how people here actually seem to use them. If they evolve into genuinely good backup solutions, only then consider changing back.