2021 New(ish) car launches.

Unless there's a breeze, wind or convection moving it the "air" doesn't do anything until the car moves though it and pushes it around. The basic difference between the wind tunnel and what actually happens when the car move through the atmosphere is the air in the tunnel has added kinetic energy while the static air must first be move from it resting place or convinced to be redirected from the path it's already flowing. It a car is sliding though a turn it's no longer hitting the atmosphere head on, there's a bit of sideways slip effecting the way it passes though the air. 

As for the flat paint there is some science about boundary layers and all that but i doubt there's enough surface reaction to make a huge difference, and the 5 or so pounds of clear coat and the time and expense it take to apply it are better utilized somewhere else.