I'm not aware of any stats, but I've experienced the difference between hot neighborhoods and cooler neighborhoods, right next to each other in Houston. It would be great to have a quantitative measure for this effect, similar to a walk score (which isn't perfect, but can be occasionally useful).
Are you sure it’s because of AC and not the amount of concrete pathways compared to green areas, vegetation and shade from trees? Also various thermal properties of the ground?
Even if houses were 50% of the land area, they take up a miniscule amount of air volume. Also, hot air floats up, so there is little chance you could feel the heat from an AC outside.
On the other hand, if the earth is hot because you have few trees, you will feel it everywhere when walking on a sidewalk.
In Europe at least it’s common knowledge that you need to have trees and greenery everywhere to make heat bearable outside. If you replace trees and grass with concrete you get an island of heat that will be unbearable during summer to walk through.