That is fair. I think you missed his subtle point though. For the person giving the millions it matters a lot if the numbers stuck up. For the hacker news bak of the envelope calculater estimates, round ups, even guesses suffice.

I think it is fair to say that while of course one should do the things you mentioned, one also would be wise to trust slightly more the "qulified" person, unless of course they want to go full blow on the matter and engage in thorough deep analysis.