I expect that's why they mentioned that it's officially unsupported behaviour. That doesn't seem too relevant to whose idea it was.

weel it's a bad idea unless you update just one package that doesn't have too many shared dependencies, things gets complicated with shared dependencies across their packages, so that's why it's better to run the full -Syu of course not automated but when you know what you are upgrading and possible manual interventions (if any) or caveats that you might have with the changes.