B-b-but muh “state polls aren’t consistent with a double digit national Biden lead” 😭
Biden's strength with olds seems to be doing a bit of depolarisation. There seems to be a curious phenomenon where he's getting extremely strong polling in red states like MT, MO, IN, even WV, while the battleground states are moving towards him slightly less decisively from the pre-debate leads.
I compared the polling averages in various states with a hypothetical Biden +9 map based on a uniform national swing, and I think what we're seeing in Indiana and Missouri is a combination of what you're suggesting here along with Biden also overperforming generally across the Midwest as well, including in the battleground states.