It's been rightfully determined BS for a while now. We used to mess with it in the early 80's though.
However coating the main lower trunks with a lindane insecticide paint was used in the old days quite successfully. Then it got outlawed.
Orchard growers still paint their trunks white. Apparently for two reason. Using a thick latex paint provides insulation from cracking/frost damage. The paint being white keeps the trunks cooler during high temps.
In addition to Oak wilt, it is also recommended for covering pruning cuts on elm for DED transmission...similar situation an aggressive fungus vectored by an insect attracted to fresh cuts. Best to avoid cutting during the flight season of the insects...but when you have to, coat the cuts.
Look to university research. They have well-controlled replicated experiments - none that I have seen showing coating works.
Sure, wound coverings have a bad reputation but they have their place in the arborculturalists toolbox. There is credible data that support wound paints. Just ask any arborist working in Wilt territory or the practitioner open minded enough to work with any number of biocontrol coverings for a specific purpose.