Hmm… It is true that only Apple provides a backup mechanism (well, apart from some of the utility software like iMazing and iPhone Backup Extractor), and I certainly have no knowledge about whether those are the same thing on different mediums or not (I doubt anyone outside Apple knows that).
I have had situations where restoring from an iTunes backup failed where restoring from an iCloud backup worked. And more recently, I’ve become unable to back up to iTunes because it claims my Mac doesn’t have enough free space. This was with a 256 GB iPhone X with about 80 GB used, backing up to a Mac that 140 GB free. That’s problematic, but since I’ve come to trust iCloud more than iTunes, it only really irks me when I want to do something major, like a nuke and pave, where a second backup would be welcome.
Well, it is the last-ditch effort, so one would hope it wasn’t expected to be common. But how did you find it to be that clunky, assuming you could restore from you good backup?
My wife and son just swapped phones (@simon, you’ll love this—it was because the iPhone X was too big for Tonya, so she gave it to Tristan and took his iPhone 7) so both of them did exactly this: Settings > General > Reset > Erase All Content and Settings, wait a little, and then set up the phone again, restoring from backup after the Hello screen. It wasn’t quick, but both managed it in an evening while we were making and eating dinner. The main downside is that I believe (but haven’t tracked down explicitly) that some settings and logins are still lost when you do this.