Hall of Fame
You're only mentioning one team, which happens to be one of, if not the, greatest dynasty in NFL history.Chad O'Shea has been NE's WR coach since 2009. O'Brien has had at least 2 in 3 years. Dante Scarnecchia has been their o-line coach for 16 seasons. How many has O'Brien had? Joe Judge has been NE's ST's assistant coach and now coach for 4 years. O'Brien? Josh Boyer, defensive backs coach has been with Belichick for 8 years, the last 5 in his current position. Ivan Fears, RB coach for the Pats for the last 15. He's been with them for 20 years.
One of the reasons the Patriots are so good is because they have stability throughout their organization. The Texans, under O'Brien do not.
OB is in his 3rd year as HC. He's said that he's going to evaluate every aspect of the team every offseason and make changes that he deems appropriate. I think he'll settle on his position coaches when he gets the production he wants from said position. I wouldn't be surprised at a few more changes this offseason.