The reason is that in the State of Ohio (until a few years ago) any non-limited-access road or highway had a statuatory max speed limit of 35, period, regardless of road conditions.
In other words...AN ARBITRARY NUMBER WITH NO REASON BEHIND IT.
Perhaps in a true “urban” setting it makes sense, but the law didn’t distinguish - if it was in a city limits, it was 35, period, unless it was an interstate-type highway.
You researched this and this is what that research discovered is it? Someone or some group got together and decided arbitrarily that the posted speed limit would be "x"? Or, is this just your personal opinion for why the posted speed limit is 35mph? Have you done any research into what/how/why posted speed limits are derived? I can't speak to every little corner of this country, but according to courses I've taken in college there is scientific studies that have been done in order to determine the appropriate and safest speed limits for highways, city streets, etc. I don't know if this was done for every roadway, but I do know that these studies have been done.