The problem is your way of circling areas are quite arbitrary. I can just extend more into downstate IL like you did into WI, or make the east cutoff westward, to get a very R number I want.
Include the rest of western WI and the WI portion is Trump +1 (east of there, Biden won by 3).
Include a southward track relative to my selected IA's bent into IL and the IL portion is tied (Trump won south of there by 29 points; Biden won Lake/Cook by 47).
So now we're haggling over a 2-3 point difference in 2020 at best.
It's not abritary other than basing it on the clustered segment of IA that comprises the vast majority
and expanding it in a north-east trajectory while avoiding egregiously larger urban areas (Milwaukee, Chicago, etc) where urbanized IA has no analog. Again, go north and/or east = things tend to become more liberal in an apples-to-apples sense; go south and/or west = things do the opposite. This also completely omits the discussion of cultural influences due to the Driftless Area, but that's not a major concern.
Most people think IA sticks out because they compare it to the Dakotas or Nebraska or Missouri. That's the wrong comparison. Perhaps eastern IA should be like 3-4 points more GOP than it is based on my metric, but that's not really enough to write home about and wonder "why?" - especially when the default concern is frankly rooted more in "why is IA 15+ points more D than Nebraska?" or whatever. Western depopulated IA looks a lot more like the parts south and west of it; eastern IA looks a lot more like the parts north and east of it - and since the latter is the larger portion, it skews the state in said direction.