Prince of Dorkness
I've been doing some thinking about this and I would be all for getting rid of the Battlemaster as a subclass and just incorporating its features into the core Fighter class. I jotted down some notes that, I think, work for both 5e and One D&D:i think more martials really ought to have their basic options open up, increasing movespeed, gaining natural climb and swim speeds, a vertical leap, yes some of those are signature traits of certain classes but that just would mean they get even bigger increases, the wizard casts spider climb to ascend a rock wall but the rogue, fighter and barbarian can just climb it themselves, the monk ran straight up it not even slowing their pace.
would martials really be broken if they all had access to unlimited use battlemaster maneuvres(either without the battlemaster die boost or maybe just a d4?), even if certain classes only could access certain ones, there's no way being able to trip or shove an enemy with your attacks would begin to rival the power of hypnotic pattern or fireball.
edit: fighting styles ought to be more prevalent too, outside of investing resources with feats and multiclassing only one subclass of one class will ever have more than one fighting style, and they get to have two whole fighting styles! wow! martial classes should really be picking up fighting styles left and right.
Combat Superiority (3rd level) – move to 2nd level
Student of War (3rd level) - remove
Know Your Enemy (7th Level) – remove
Improved Combat Superiority (10th & 18th levels) – move to 9th & 17th levels [Enhanced Combat Superiority]
Relentless (15th level) – move to 13th level
So you would add the following to the Fighter table:
2nd level – Combat Superiority
9th level – Improved Combat Superiority
13th level – Relentless
17th level - Enhanced Combat Superiority