As you’ve deduced, iCloud backup for an iPhone is really less of a backup than simply a “most recent copy.”
[and the iCloud sync function for many apps (e.g. photos) behaves in much the same manner, albeit almost continuously]
At the risk of guessing Apple’s intent, it’s primary purpose is likely to allow the vast bulk of “Most” users to nearly painlessly - and w/o any preparatory effort - restore a replacement device to “match” their prior device when that need inevitably arises.
A more “classic” backup solution (as has already been posted) and which provides more capability to the more “sophisticated” users …
… requires the use of a cable and computer.
See additional info here:
What does iCloud back up? - Apple Support