I think the Battle Master Fighter needs a bit more, let’s add some via a feat.

 

Battle Mastery

You are the god of war knowing how to make any weapon do what you want them to.  Gain the following benefits:

• Double your proficiency bonus applied to your Maneuver Save DC.
• When you gain an extra superiority die at level 7 and 15, gain two instead.

 

Thoughts?