Look at Pathfinder 2:
The Fighter's entire schtick is getting +2 to attacks that nobody else can get.
That's how I see the fighter. More fun and compeling.
* a flat bonus to attack with weapons that improves at certain levels.
* add proficiency bonus to damage -- as the fighter gain levels your attacks become more deadly.
* add compeling combat styles as archetypes: gunslinger, iaijutsu master, polearm master, etc.
* add core features that reflects the foghter Identify: armor benefits, block attacks, ignore pain, resolve, resist exhaustion, etc.
* keep second wind, but add buff to it: maybe when you use second you can spend HD to gain more hit points.
* higher critical chance: roll a critical is fun.
* maneuvers as baseline for every class, but fighter can use the improved version.
* the fighter should be a able to gain more attacks based on a maneuver, or combat style feature he uses, instead being limited to action surge.
* group utility: extend a core ability to a group member (shot, order, or "as long your froup follo your instructions")