Please explain how these map of partisan primaries are informative?
No one said that they were informative. They're just interesting ways of looking at the shares of how much one party turned out in contrast to the other
It's a good way of viewing long-term institutional strength. Especially since you have voters in both parties that are with the one party local and state level, but not federal. My rough estimate is 10% of the voters in North Carolina in the '80s, '90s, and '00s were "Democrats state and local, Republicans federal". That group pretty much decided who won every election.
Also seeing Democrats win some of those traditional down-ballot Republican suburban/urban counties like DuPage, IL, Chester, PA, Gwinnett, GA, Harris, TX, Hamilton, OH and Morris, NJ is striking.