I've had really strong fruit set on almost all of my trees, and I've had zero powdery mildew. The keys this year for me have been strong potassium / nutrient levels and consistent application of fungicide.
The lot where my house is has a good amount of potassium (per lab report) from about a decade worth of ultra heavy mulching (> 1,000 cubic yards). The adjacent lot where the soil is basically just loamy sand with no organic material nor fertilizer has had sparse fruit set on all but the workhorses (eg, Angie). Nitrogen on the mulched lot appears to be a little high and contributes to a little more growth than I'd like, but fruit set has been really strong.
Weekly misting with copper + sulfur has made a dramatic difference in fungal infections -- even more so than when I was using a sprayer. Coverage seems to be better with the mister.
In my experience, the key to mango production in my area is funcigicide application and good nutrient levels.