You post this like it's an excuse for the Texans. First taking a mandate from Derrick was dumb. Second, even if there was a mandate. Was Culley a better option than Leslie Frazier or even Jim Caldwell? Exactly what would Culley bring to the table to impress Derrick?
If Caldwell is selected, one of the first people calling Derrick would have been Peyton Manning to tell him what a great offensive coach was hired. With the 2020 defensive struggles, players who were coached by Frazier could call Watson and tell him what a great defensive mind was hired and how he would improve the defense. Who would call Derrick on Culley's behalf? A spokesman for Hubba Bubba?
Yes the McNair's are dumb people. Just remember when you hire somebody, you have to think about how it's going to go down when you have to fire them. Culley was the path of least resistance.