Let me propose this theory regarding the firing of Flo.
Let's look at the history of some Billy's Kids once they leave New England:
Josh MacDaniels
He went for total control early. Traded Cutler which was good, but drafted Tebow in round #1, which was a joke. Ran a playoff contender into the ground. Got his *** fired and ran back to Daddy leaving Jon Elway and Peyton Manning to temporarily right the ship.
Bill O'Brien
Gained total control. Made some playoff appearances. But, ran the franchise into the ground through some of the worst trades in NFL history. Ran to Billy's college clone and hid out for a year. Now looking to re-enter the league.
Joe Judge
This guy can't coach his way out of a wet paper bag with a hole in it. Failed at coaching so badly, he never had the chance to attempt a play for total control.
Brian Flores
Great coach. Players played hard for him. Back to back winning seasons for the first time in how long? BUT: His relationship with Grier soured for some reason. Was it Tua over Herbert? Was it wanting Watson? Who knows, Who cares?
My theory is he decided he couldn't work with Grier any more and wanted total control or out and forced Ross to choose.
Moral of this story?
If you try to slice your GM's throat, make sure the team owner is on board with it or you will be unemployed.