I'd like to see Leadership added as a skill, and give back the fighter the ability to accumulate followers. The Leadership skill should be usable both in combat and the other pillars - organizing individuals, predicting enemy tactics or weaknesses, political use (Persuasion = changing folk's minds, Leadership = getting them to act), bettering troop morale, recruiting followers and the like. I also think it would be a great skill to dangle Warlord/Marshal-like abilities off, where the fighter's Leadership can modify the ebb and flow of a combat as they maneuver or motivate allies, hone in on enemy weaknesses and the like.
Also, fighters - not just Battlemasters - should be the king of Bonus Actions and Reactions. I'd like to see more "hit point damage and a rider effect" options for fighters, utilizing their bonus actions. Also, more defensive options with reactions, especially ways to use armor, weapons or shields in ways most of the other classes can't