They were tough, and they had low life expectancies; that is why I am so skeptical of high population estimates for them. I’d recommend reading the original “Little House on the Prairie” books to anyone interested in getting a feel for life on the plains; unlike the TV show, it was an autobiographical story by Laura Ingalls Wilder, and you get a real understanding of the hardships suffered by the original settlers in those areas.
The descriptions of children freezing to death walking home from school due to blizzards, or remaining in the schoolhouse burning all of the furniture while they wait out the storm, are incredible...
Your description is accurate. Most modern Americans would not last a season living under those conditions today. Few people have the skills and determination to do what our ancestors did. Also, the summers are hell out there on the Plains. Even in the Dakotas many 100 degree days in a row is not uncommon. Combine that with little rainfall, and it was easy to go hungry and get discouraged.