The mechanics don't really make fighters. You could have a group full of battlemaster fighters and give each one a very different flavour just through stats, equipment, background, manoeuvres and personality.
The sense that they are weak is illusory because they don't have nova capabilities. Much of the nova damage is often wasted though and the other classes can't do it often.
Someone on here proposed superior manoeuvres that cost two dice and have beefier effects but they'd need to be limited as not every subclass uses them.