Most interesting Bluebell, especially about the soil temperature because I have always noticed white rot more in May than in June, and my overwintered onions being more susceptible. I have stopped growing them because they also seem more vulnerable to downy mildew which then spreads to spring-sown onions.
I do very little hoeing and raking and noticed at Lower Farm how the white rot never spread at all, staying very localised in only a few small areas, and I never worked out how it had got there!
As for stronger plants surviving, that is hopeful as one imagines these diseases wiping everything, as with late blight on potato and tomato.