I don't know the details or have a clue, but i can imagine, it wasn't about freedom.
It may have been more about autocracy over the desgin.
Mclaren looks to me like a "teamwork" team, splitting the car's design into different work groups.
In Newey's case, i think his car's are conceptualized by him and him alone.
It's designed and then tossed down to the little worker ants to realize.
I don't think he likes the "work as a team" moto on his cars.
Just like how some super car engines are built with one master builder.
He does the total design and the other guys engineer the systems and do the failure tests.
As for Byrne, someone should post all his cars. I don't think he'll be on top of his game now. He could be an over hyped dinosaur. You need to be in the game to evolve with it.