Not just December gun season, it's shotgun. Everyone thinks Buffalo County, WI is so great because of supposed "minerals" in the soil because it's in the Driftless Region. In reality, they have more or less the same genetics and nutrition as any other similar county along the Mississippi River. the reason they have such great hunting is because they were shotgun only until recently. QDM is well practiced there and thats why they maintain the good bucks. Iowa being shotgun only will always keep the number of older bucks higher than in states that allow rifles for gun season.
The days of being able to hunt lightly pressured areas and see a 150" behind every tree are in the past. Whether anyone likes it or not, Iowa has the attention on it now, partially because the DNR whored out the deer with Governor's Tags. Demand in Iowa probably isn't going to down, especially with both recreational and ag ground both being in high demand. If anyone blames non-resident hunting pressure, they're misguided. Have you guys forgotten about the early youth muzzleloader and the early muzzleloader sesaon for residents? Liberal seasons and bag limits have had a much larger impact on any perceived quality degradation in Iowa deer hunting than NR/NRLO's.