I’m thinking your based question is “Does wind tunnel testing actually help?”
Seems the only method for figuring this out is using a more “large-data” methodology. Overall, have cycling speeds increased /w/kg over the last twenty years? Take the top ten pros at each race and compare their power (provided or calculated) and speed numbers over twenty years.
This won’t be exact, of course, but it will indicate whether wind tunnel testing is having an overall impact on the sport.
Whether it has a specific impact on a specific athlete is kind of irrelevant (IMHO), and is as easy to calculate as calculating where a hurricane will hit land in three days. There’s two much data to gather to calculate, and most of the data needed is not available. Something as tiny as where someone rides on the road would have some effect if the road is not a perfect road.
So, if overall times have come down proportionately to any increase in w/kg, the answer is “Yes, it’s made a difference.”