The amount of NFL coaches who have control of the 53-man roster is short for good reason. Not everyone can handle that much power.
Houston Texans head coach Bill O'Brien, who has the final say on transactions, as the team currently operates without a GM, has proven recently that he isn't cut out for this. After overpaying in a trade for Laremy Tunsil and Kenny Stills, while flipping Jadeveon Clowney for nothing, O'Brien cut cornerback Aaron Colvin, in the second year of a four-year contract, after a bad game against the New Orleans Saints.
That's why GMs are in the position they are in. They can be more cold and calculating than a fiery, emotional head coach. It's also why Bill Belichick, the coldest and most calculating of them all, has been so successful in his dual role.
O'Brien is officially a tyrant in Houston, and is throwing caution, financial security, and the team's draft picks to the wind in order to win now, which is extremely unlikely, given that offensive line.
Hope you win the Super Bowl in the next two years, Texans fans. If not, this team is set up to be near the bottom of the league due to some bad contracts and a lack of draft picks.