I think you are getting bogged down in how 'unknown' an 'unknown quantity' has to be before we put 'relatively' in front of it. That's a linguistic consideration that isn't relevant to my broad argument.
Ten Hag had a good CV on paper. But it wasn't amazing, or special, or unique. Manchester United should be able to find candidates with similar combination of skill + experience + potential. They will have weaknesses, but hey, so does Ten Hag.
Ultimately the argument is simple, you rate Ten Hag, other people don't rate him much anymore. There's no broader principle behind that. If you are a Redcafe poster who thought Ten Hag had potential, and no longer think he has potential, then any manager who has potential is a better option. If you still think he has potential, then that is no longer the case.