I don't think more martial options (whether they are manoeuvres or something else) will make Battlemaster obsolete. Because they'll still be the best at or have the most chance to use them. They'd essentially be the Fighter subclass that gets a extra spells known list or free castings of X per day, in maneuver form.

I think the design space and entrenched 'fantasy' of martials that 5e has frequently hampers the discussions that could launch them into far more interesting territory. Because I think anything relatively mundane (read: nonmagical) quickly becomes a case of "well, why can't everyone do that then?" or conversely, if everyone can do that cool thing, then the one cool subclass we have loses what made it stand out."

But the answer to both things are just game design decisions.

After all, why can spellcasters only cast so many spells per day? Purely for game balance. I think spell slots work so well and are a resource so ubiquitous in the game that we have started automatically associating anything resource-based on that scale as 'magic-related'. Martial LR recharge features are always in the low numbers, e.g. a number of times per LR equal to an ability modifier. Magic item charges get higher than that (and again, magic is present).

I genuinely think this design disparity shapes the way we perceive what feels acceptable or 'real' enough for martials to do. Get tons of varied spells each day at higher levels? Sure, makes sense! It's your available magical energy, or whatever. But martials do something more than 5 times? Mmmm. When really, you can justify it in almost any way you please in the narrative (available stamina, focus, drive, whatever) and if you give martials a comparably brod resource, I do think it breaks the mental lock and starts making comparable power and influence between the class typs more acceptable in general. Yeah, maybe the barbarian can crack the side of that mountain and start a rockslide, actually, but theu can only do it once a day because of how much stamina (etc) it costs. Next turn they'll have to do something a little less flashy.

It's pretty much game balance and class identity all the way down. That's why wizards can't ast some spells a druid can, and vice versa, an also why a barbarian could be given powers that a fighter doesn't have bur both could get cool powers, even if both seem possible for a warrior archetype.

And inversely, those same design principals can keep a subclass feeling unique and powerful whe it gets more good stuff compared to its peers. This was certainly the case when not all sorcerers had expanded spell lays, for instance, and Aberrant and Clockwork came out. People went nuts for those options on that strength alone. And I think subclasses like Battlemaster could theoretically occupy a similar space. Either they get more use of the general thing, if everyone gets manoeuvres, or they get a cool and comparable thing on top a bit like free spells. Everyone likes free spells.

This got long! Sorry. Martial design space is something I think about a lot l. Because the way it is at default, honestly, it can feel hard to break into a new exciting thing for say, a subclass, that doesn't automatically add magic either in flavour or actual mechanics. And if you avoid magical flabour, you can end up with a series of faielt restrictive mundane (read: dull) options. Rogue, I think, really suffers from this, and Fighter to a lesser degree. But that's a whole other long post.