I don’t think your stats include all the games. This is the defensive stats that include UFs 12 games and Texas 10 games. You may want to check your stats again. Maybe the stats you are using downs include the bowl game. The Texas defense was substantially better in yards per play which at least IMO is a very important defensive stat.
So statistically Ash’s defense didn’t perform worse than Grantham’s and the yards per play for UTs defense was 27th in the country vs UFs at 85th in the country.
Also the Texas defense improved from 2019 to 2020. Unfortunately your statement is not true and not supported by facts.
The even more important statistic to me is how much the Texas defense improved from 2019 to 2020 considering no Spring practice & Covid and the offenses generally being a step ahead this year across the country. Ash is a top notch DC