I thought one of the issues with potatoes is that they have a really high glycemic index, not lack of nutrients.
So consistently eating a lot of them increases one's risk of Type 2 diabetes.
This is true. Most of the potatoes eaten are valuable in caloric-deprived situations, but they are not a long-term healthy food due to the thrashing they do to insulin management.
The Danes (maybe all Scandinavians?) eat potatoes with almost every meal. Do they have a higher incidence of diabetes?
That is misleading. Potatoes are ranked as one of the most satiating foods per calorie. The problem is people put a lot of butter/oil on them. Or eat them too processed.