The subclass itself is fine, plenty of people enjoy it. No problem there.
But we just got a book full of magic options, and we're not getting a martial equivalent. The monthly D&D Beyond drops give us new spells, and never new martial options. The reason why is obvious - you can always add new spells, but there's no way to expand martial options the same way.
And the main reason for that is there are no maneuvers or anything. That's how D&D originally solved martials lacking interesting choices, a couple of decades ago at this point, but in 5e they named a battle master feature the same thing despite being a minor, really limited system and only belonging to one subclass.
Now whenever you mention the idea of adding maneuvers to the game, people immediately jump in with "uh, we don't need that, haven't you heard of battle master?". Which is like saying rune knight exists, so we don't need spellcasting classes.
So yeah. Subclass itself is perfectly fine, genuinely adds much more than your average subclass really, but it existing at all has hobbled and blinkered both design and discourse regarding martials. I'm fairly sure that if it had never been created at all, we'd have gotten some better solutions by now - but it looks juuuust enough like a solution that people instead say eh it's solved battle master exists.
unstablez0 - D&D nights
Nat 1s are character development.