The key part of the deal is that ESA and Arianespace will be ceding ownership of the rocket to Airbus Safran.
The French government is likely to approve the sale of CNES's 34-percent stake in the Evry, France-based Arianespace launch service provider to Airbus Safran Launchers at about the same time as the Ariane 6 development contract is signed.
With that sale, Airbus Safran will control Arianespace, which means they will also own the rocket they are building for Arianespace. This is fundamentally different than the situation with Ariane 5, which Airbus built for an Arianespace owned and run by the many-headed ESA. The result was a bloated government-run operation that never made a profit.
Now Airbus will own it instead. They have already indicated that they will trim the costs at Arianespace. More importantly, with ownership will come the freedom to compete effectively in the much more competitive launch market created by the arrival of SpaceX. No need to get permission from ESA to do things.