FoxEye,
it should be perfectly obvious to any tech that in certain situations a partition is useful, there is no shame in creating a partition if it can help make life easier.
Your objection to this is a rather contrived example of a low level user using a single drive computer which has been configured by an inept techie who hasn't partitioned the drive correctly and hasn't mapped all the user data folders to the correctly proportioned data partition, and yeah in this "Theoretical" your absolutely right its causing more problems than its saving . . . . however that's not the situation I had in mind!
In your example what is going to happen should, heavens forbid the low level user plugs in a USB drive!? . . . how will they ever get their head around the concept of another drive just appearing, it will be like a UFO just landing from space.
So with all that said I think you are just not getting this whole partitions and custom backups thing, most techs probably have multiple drives and I'm sure even low level users are now getting their heads around multiple drives, especially if the new users have a kick ass mate who knows what he is doing and can explain basic file management and drive structure to them.
Partitions in reality mimic a separate drive albeit large copy and pastes take a lot longer as do backup and restores but in certain situations it is just useful if you can move all the important user data off the system partition so you work on the borked OS with no worries.
I understand your point about being able to nuke Window's 10 from orbit and end up with a clean install but that is still not good enough. As a techie I don't want to be dealing with a Virgin OS more than once and this is the beauty of custom backups sitting safely on another drive or *partition*
Instead of being lumped with a Virgin install a basic computer user can "Restore" the OS from any snapshot they like, Windows 100% updated, tweaked, all the users applications games and software installed, all the plug ins, all the preferences, patches, tweaks . . . . that's quite a lot of work and it's so boring to do more than once hence the reason for carefully making backups and sticking them on another drive and if there is no other drive then a partition will do a very good job.
There is nothing you are stating which will make me change my position on this but I hope some of what I am saying sinks in a little with anyone reading because it's something which could keep you out of trouble or save hours in the future and that can only be a good thing.
In the situation I am describing where a single drive is partitioned into two, the tech knows how much data they have and are likely to have and they also know roughly what programs are to be installed. You always leave plenty of room for the OS and apps but then dedicate the rest to user data. In Windows 7 its a 5 minute job to remap all the colourful icon user data folders over to another drive or partition but I don't know about Windows 10?. On Windows 7 the whole process is transparent to the end user, they still install programs and software to the default C: location so no change there and they still save their downloads to "My Downloads", they still find all their office work in "My Documents" etc
Your concerns over what I am suggesting don't seem to be legit but if you're still not seeing the light on why it's so advantageous to be able to "time travel" your system back to one of several predetermined times when it is rocking then I'm too tired to paint you anymore of a picture, vanilla installs in times of trouble is not the best way, having user data mixed in with a failed OS is no fun at all, maybe when everyone is running Windows 10 special nuke edition things will be easier but bespoke O/S backups are still a techies best friend and a super timesaver and if they have to be stored on a partition along with "My Documents" then so be it, O/S backups and Data backups are two different things haha!