Why over-complicated? I'm genuinely curious, as I think it sounds pretty cool that you can install apps from different package managers in containers, but export them to use them in your main environment.
I briefly looked documentation, all the tools they provide, etc. Why we need supporting both rpm, deb and own format too? Why Debian? A/B is better than btrfs or symlinks? Maybe I should read documentation more, but why? It sounds really complicated with too many whys (and whay more why's even compare to NixOS, being hardcore, but plain simple why).
What are updates if it is Debian Sid? Updates to software will replace A and B? Or do you install everything to A and B replaces A only with next OS update?
Looks bad in comparison with Silverblue where I can pin many previous version. Thanks to OSTree, you can downgrade to any point in the history or even switch back to an older release.