I listen to the F1 podcasts, Beyong The Grid w/Tom Clarkson. He has drivers, team principals, mechanics, designers, etc on for interviews. Some of the guests were around for both the 80s/90s and more recent. Listening to them talk about how dramatic the changes in design they've had just because of the wind tunnels and data acquisition programs is incredible.
Basically, up until about the last 15-18 years, they were completely guessing on the airflow. They'd make a change, see how the car ran, then decide to keep it or not. If they missed b3fore the season, it might take the entire season to fix it.
Now, they run it in the wind tunnel, get the data, make tweaks, put the upgrade on the car and go. The difference between the best and worst teams is the cost and availability in the airflow data.
Now, I haven't looked this year to see the difference in average times between the top and bottom teams, but it "feels" closer than in past seasons, so maybe the new regs have minimized that.