Think you're getting a little over-enthusiastic there. DeSoto probably didn't get any farther north than the MO bootheel.
Also the country he traveled thru is described as heavily populated, which no doubt explains to some extent why it was "open." Also large populations don't go along real well with desert conditions.
Did you read what I said ~ depending on how you read it.......
There's an older view that has him cross South of the Ohio ~ but at that time *(1541) that wasn't separately named.
Note, big note too ~ 90% of the main flow of the Mississippi at Cairo comes from the Ohio. The Northern branch is of little more significance than the Wabash!
His diary clearly describes the fish pens at Terre Haute, the surface iron pyrite in SE Indiana, the Indian village at Angel Mounds at Evansville.
What more could you want?