From what I have gathered from speaking to a farmer friend, you are quite correct about the amount of spraying, Eric.
From what I gather online, they don't use the same spray each time - they have to spray for different blight strains.
Farmers would need to be biologists
I used that same mixture throughout my spraying program and managed to get away with it.
One of I'm sure a number of reasons you don't use the same ground each year is to ensure any of last years spuds don't grow again as they might have blight. Thats why seed need to be certified.
Even the smallest spuds can grow again. They need to be destroyed as they emerge, or if they sprout up on a compost heap.
Next year, I may adopt your advice- to grow earlies instead. As you have stated, they are almost fully grown before the blight conditions happen, so less spraying required.