Find yourself some new experts. You're already showing your using your noodle more than they have. The reason for having adjustable idle mixture screws is to adjust them. The number of turns out is not the way to determine what the engine needs. :rolleyes: As you observed, its clearly too rich for your engine at just one turn out.
As long as the engine responds to the adjments, its not terribly important if they are 1/4 turn out, 2 turns out or something in between. Keeping track of the number of turns out is useful but it's not a target.
With a four corner idle, the manifold vacuum is acting on a second set of idle ports and supply. This is why 4 corner carbs generally need less turns out on the mixture screws. Compared to a similar carb with 2 corner idle, it doubles the idle port fueling. So if the engine produces reasonable decent vacuum at idle, having them end up at less the 1 turn out is not surprising.
PS. Sadly its not not the first time I've heard of a professional give this type of advice.
PSS. Judge best power at idle by using rpm and vacuum in gear if an automatic. Your AFR gage may or may not be terribly accurate at idle depending on the reversion and quality of the burn.