I have to re-read what her system is but would that work indefinitely in an area with a high incidence of blight? There's a farm around here that had to stop their potato coop program after 20 years due to blight. They also had to buy new seed for their market garden.
I have no bias against potatoes! I have no bias against annuals, either. They are a problem when planted exclusively, in over-large groupings, and when not rotated, is all. For learning to breed, there is nothing better to work with because of the quick turnaround -- Norman Borlaug, famous/notorious hero/villain of the Green Revolution made rapid progress with wheat by running seed back and forth between two breeding stations where the planting season for one started right around the harvest season for the other, so he got two crops in per year. They use fruit flies to study genetics because they have a two or three day lifespan. Annuals are the fruit flies of the vegetable world (radishes are probably the fruit flies of the annuals world). And they are often delicious, with fascinating backstories, and hundreds or thousands of local varieties developed over hundreds or thousands of years.
The venerable Ms. Deppe says blight is an everpresent reality in most places, including where she lives. PP.168-9 of her book tells you how to deal with disease, in general, including blight. The short of it is rotate your fields every year and leave at least three years between planting potatoes in one spot, cull out nasty looking plants the moment you see them, start with certified seed potatoes and then rigorously maintain a selection program (detailed in her next section), don't leave cull potatoes in the field because they will harbor diseases (including blight) remove or till under residues, wait a couple weeks to harvest after the plant tops are dead and gone, that way blight and bacterial rot will rot the bad potatoes, revealing them as the sinister agents of destruction that they are. And she notes that early maturing potatoes can beat late blight.
It seems like a lot of work, no? I think growing your own staple crops is a lot of work, considering their relatively low cost in the store, but I love to do it, anyway.