Being able to roll back updates/upgrades that go wrong, is not just fixing a minor inconvenience. There's also something about the critical part of the system being less mutable. Desktop Linux has been way too easy to break in the past.
Absolutely wrong.
Tumbleweed is a conventional distro. You're root, you can do whatever you want, you have full R/W access to the entire FS, and updating is by installing lots and lots of packages into the live OS while it is running.
Aeon and Kalpa are immutable: the root fs is largely R/O even to root, and you cannot install or update packages on the running system. To install packages into the OS itself you must reboot, and installation is transactional -- it can automatically undo changes that prevented a successful boot.
Kalpa is the KDE desktop version of MicroOS.
Good explanation, but note that Tumbleweed can use transactional-update with btrfs snapshots like MicroOS. Updates are still applied live though.