iOS even restores your open applications and task manager state when you restore from the backup. Even more so, theoretically, it can restore every apps state at the point of backing up. It's a feature ported from macOS.

There is no way Apple is going to let 3rd party could providers do backups directly. I doubt exposing the iPhone as a USB device over the internet with a VM running iTunes would work efficiently.

1) You don't want to risk dumping a mounted filesystem because of inconsistencies

2) Good luck getting the right device - in the end it's devicemapper all the way down with a lot of layers (ecryptfs, sdcardfs, bind mounts, ...) stacked between your shell and the device.

3) Unrooted phones don't allow access to raw Unix devices

4) You can't restore these backups anywhere if your phone (like almost all, I think it's a Netflix requirement) uses hardware key storage - simply because the key is in the secure element of your phone. Rooting a Samsung phone kills the HSM and switches over to software key management though.

5) Assuming encryption keys don't get in your way, you can only restore the dump on exactly the same model and firmware of device you have, because every manufacturer does stuff slightly different.

To root "well made" phones, you need to unlock the bootloader, and this will erase the data on the device, to prevent data theft or compromise...

It's a bit messier if your data also lives on an internalized sd card.

Apparently this is false, because apps can "opt out" of ADB backup and many do (see other comments), furthermore it doesn't backup the entire phone, but only the system image (partly). Does it backup the root state of the phone? Nope. Does it backup the restore partition of the phone? Nope. Making it a "maybe full system backup but not full system image backup that is kind of buggy". In other words, like I wrote earlier: not a -full- system backup at all.

I was specifically talking about effortlessly backing up and restoring a full system image. Blackberry OS10 style: plug in phone, press "backup system image" and get a carbon copy of EVERYTHING that runs on the phone that can be restored to a new or existing phone with 1 click. Your post confirms that this is not possible in Android: using ADB is not "effortlessly" and it's not a full system image backup.

Even if I would backup and restore from and to the exact same rooted phone (that's all I'm asking), the restored backup would not be the same as whatever was on the phone when the ADB backup was pulled. Nandroid can do this, in theory, with a lot of hassle (but not on my phone, because TWRP for my phone doesn't support decryption of the system partition).