Mildew does come even before end of season if conditions are right. Last year with hot weather and drought I had mildew taking over late july well in growing season. Almost all cucurbits had some. This year have barely had any even this late even though temperatures might not have been ideal. Watermelons, melons and cucumbers succumbed before any signs and otherwise there are just single leaves. What I read after last year is that it likes dry weather which would make sense. It might be that plants are weaker then, but it just might be to do with it’s reproduction. Haven’t looked into it that closely. Generally plants tend to be weaker if they have heavy fruit load and they do prioritise producing seeds over staying alive. So later/less producing might seem healtier, but it’s likely not because they are more resistant.