> The argument is correct, or it isn't, no matter who said it.

Yes, but we all have insufficient intelligence and knowledge to fully evaluate all arguments in a reasonable timeframe.

Argument from authority is, indeed, a logical fallacy.

But that is not what is happening here. There is a huge difference between someone saying "Trust me, I'm an expert" and a third party saying "Oh, by the way, that guy has a metric shitton of relevant experience."

The former is used in lieu of a valid argument. The latter is used as a sanity check on all the things that you don't have time to verify yourself.