But you're not giving them as many maneuvers as a Warblade or Crusader, right? So they need something to make up for that, and in most cases their non-maneuver mechanics are fine for that. At 20th level, a Barbarian's Rage is giving him +4 to hit and +4 damage. I don't think that's a worrying amount of power. Moreover, I don't think maneuver's primary strength is damage output, and I think that allowing optimized characters to be more powerful is probably good -- it's not like you're going to end up better than a comparably optimized caster, so overall the balance is getting better.
They're also vulnerable to things that attack common spell effects. The Diamond Mind save replacers are a good example of that. Having the ability to (basically) auto-pass saves is an ability that has very obvious utility for someone fighting spellcasters, while still being useful against a variety of other opponents. Energy resistance is another example. Though ultimately, I think that's probably an argument for just adding some additional Diamond Mind maneuvers. No need to create a whole new discipline.From the SRD link, it seems they're only vulnerable to Opportunity Attacks, while regular spells aren't capable of being used in the first place when Grappled, Silenced, or under a variety of other incapacitation. So the main counterplay for Martials is there, but only that one, with Grappling accomplishing nothing.
That seems like far more complexity than should be associated with a discipline directly. Hacking a bunch of extra resource mechanics on top of a subset of maneuvers (rather than making them a PrC) seems like it restricts character creation for relatively little benefit. What if you want to make the Iron Heart/Stone Dragon/Anti-Magic guy? That seems like a reasonable build, but if your anti-magic abilities require spell slots, it won't work properly.(re)gaining slots for successfully screwing over casters rather than added bonuses for going after them. My suggestion for self-fueling is each Maneuver known giving a spell slot of half its level rounded down, and each Stance giving two such slots. These slots would, due to not being associated with any class, not be usable for actually casting spells, and I'd try to make the Discipline's methods of dealing with it favor Spontaneous casters, like a Stance having wording along the lines of "As you cast a spell, you may reduce the slot adjustment of applying metamagic to it by expending additional spell slots".
Do they all need to be combat abilities? One of the things I disliked about the original ToB was that there was no mechanism for e.g. a Shadow Hand Swordsage to have any shadow powers that weren't directly used for killing people.Not actually very well sold on Divination effects on reflection, since they're a bit hard to work with as combat abilities