Of course, sometimes failures do occur, but that happens whenever you do a major OS upgrade. I've had Windows fail on upgrade more than I've had Ubuntu fail on upgrade, but that's just my experience.
This in comparison to, well, Elementary OS saying scrap it all and reinstall. That wouldn't be so bad if they were, like, a technically-minded distribution - but for their primary market who hardly knows anything about updates, completely unacceptable.
ps: I agree with your point about EOS trying to make things invisible for the user and not addressing this well though.
https://ubuntu.com/blog/how-to-upgrade-from-ubuntu-18-04-lts...
Distros like Ubuntu make upgrade failures harder to work through because they go to some lengths to wrap the dist upgrade process in some software that reverts everything if anything goes wrong.
But if you just move all your apt sources forward to the next distro and read any specific error messages you get, you can generally work through them.
Distros other than Debian itself don't typically recommend that you do things this way, and instead have some extra software for going through the process. But the Debian way still works on them.
And it wasn't my personal machine so it would've been unreasonable for me to do so.