thatswhy there is transactional-updates etc with snapshots and if something is F up just revert or is installer isint succesfull on update it reverts back automatically and yes there can be still messed up stuff but then comes backups especially all home backups so it can be easily recover from recovery part and just roll all back from backups.
there has been lots of improvments on “immutable” now days they call it atomic since you can manipulate still the base so it isint fully read only and development takes time and how that has grown is really good