Okay 6 encounters... with 2 short rests, let's assume 3-4 rounds of combat in each encounter... so 18-24 rounds of combat
level 3: 4 Superiority Dice/3 maneuvers... 2 rests means a total of 12 superiority dice... so in 18-24 rounds of combat you will be performing 12 maneuvers. That doesn't seem like a bad refresh, the worst is that you are using a maneuver on average...every other round, the worst is that you are using a maneuver 2/3rds of the time. What rate do you think would be better?
As for your second point... choosing a maneuver doesn't waste a die since you don't commit dice to maneuvers until you actually use them. Maneuvers grant versatility.
Not much versatility. 3 maneuvers is very little when compared to the spell list of a caster. They tend to have as many cantrips as that by that level. Like I said, I consider Riposte, Precision Attack, and Trip Attack to be such generally useful choices that you'll almost always take them (unless you're a bow-fighter, then you will likely skip Riposte).
Consider. The Sword Coast Adventure Guide cantrips "Green-flame Blade" and "Booming Blade" are weapon-based cantrips that have effects that are very comparable to the effects you might expect to see on maneuvers, but they are at-will and having scaling damage. It's not a perfect comparison for a variety of reasons, but it's enough to leave a sour taste in my mouth. Sweeping Attack to Green-flame Blade. I mean, come on.
Hmmm... but depending on attribute scores, skills, prof w/certain weapons & armors, etc... everyone may not be able to do it, or at least not as well as you can. For example in most cases a 20 strength fighter is going to be able to pull off feats of strength that an eight strength fighter
Not as big as a gap as you might think, given the oft-quoted problem with bounded accuracy and ability checks. Being proficient in something doesn't actually improve the odds of success that much. In very extreme cases, like an 8 non-proficient vs. a 20 proficient, sure, there's a noticeable gap. But that's more of an outlier than a useful example.
You didn't really answer my question though... what space are we looking to fill here? What things specifically are we trying to give the fighter that...
1. Are not covered by a current maneuver
2. Are not narrower or weaker than the current maneuvers
3. Are within the realm of doing martial things (as opposed to spells disguised as maneuvers since that's what the EK is for)
I gave one specific example of such, actually: grappling. Grappling is not covered or aided by any maneuver. And it's definitely a combat-oriented concern. You could boost grappling and shoving by aiding Athletics checks related to specific actions (Grappling, Shoving, Climbing other creatures, etc), and it wouldn't even interfere with a non-combat pillar, though I don't think it'd do all that much harm if it was a general boost to Athletics.
As for the optional rules in the DMG... I disagree. If the group wants that level of granularity in combat then it will be included... otherwise forcing it into the game just limits your audience since those who don't want it as part of the game will have a harder time removing it if it's core.
Anything that would be hypothetically released at this point
wouldn't be core.
What "tools" are you looking for? What exactly in grappling (within the 5e rules for grappling) are you trying to accomplish? What tools do the barb, rogue and bard have that make them better grapplers? As long as you have a weapon in one hand all of the BM maneuvers are useful during a grapple and even without a weapon there are some that can be used... but I'd have to know more about what you can achieve from those other classes that you can't with the fighter first.
Rogue and bard have expertise, which doubles the proficiency bonus to Athletics. Bards can increase their bonuses on top of this via Enlarge/Reduce or Enhance Ability, 2nd-level spells. Rogues have Cunning Action, which can be used to Dash, and therefore increase the distance you can drag targets while grappling (remember, when you have grappled another creature, you can move at half speed, and move the other creature with you). I consider that to be quite important because the grappler focuses more on controlling the flow of battle than huge damage, and grappling opponents so you can drag them over to a cliff side and shove them off, for example, is one thing you can do with that (or into pits, into harmful spell effects, etc). The barbarian can Rage, which gives them advantage on all Strength-related checks, including Athletics, and get a minor boost to speed besides.
All three classes have innate ways to improve their Athletics checks, and the bard and rogue have significant additional advantages besides that. The fighter cannot boost its Athletics check on its own, the best it can say is that it can Action Surge for additional movement/tries every so often, or it eventually scales up to a large number of attacks for more attempts to grapple (has to wait a long time for that though).
This seems at a glance, on top of the fighter's other abilities over powered... Only one is new design space and it gives the fighter a gigantic boost in the other pillars while letting him keep his already formidable combat prowess as well... The others just seem like better versions of what exists but then my question is at what point is it too good. Combat wise I have 2 BM's in my current game and nether one seems to need better abilities in combat.
I would not say the battle master is
bad balance-wise. I do think it's a bit weak, and I think it'd be evident if, say, I were to temporarily allow a battle master's superiority dice to recharge at the start of each turn. As far as the dice recharging at the start of each turn goes, it was actually like that for a significant portion of the playtest, and didn't seem to break anything!
But that's just a thought experiment. Maybe it would go horribly wrong. I doubt it, but maybe.
Okay so at what point are we intruding on the niche of the monk as the "mystical warrior"? Or the EK which seems to be the fighter for those who want to do what magic does? It seems you want a different design ethos encapsulated by 3e and 4e moreso than 5e... a bunch of fiddly narrow options as opposed to fewer broad options... not sure I want to see 5e go down that path... at least not in core.
I'm not proposing any more "fiddly narrow options" than the spell list provides a full caster. I would actually use the EK or perhaps Paladin as a baseline if I was to design the class myself, but with its own list instead of simply drawing in a limited form from the wizard list (or having the paladin's focus on buffing/healing).
... Really, though, it's not as simple as all classes getting to improve all the same stuff, making it a wash. On the one hand...
I know the issue isn't as simple as all that, I just didn't really want to get in-depth into it, because I have a feeling the horse is kindergarten paste by now.
Agreed. While a limited-use maneuver that attacked all enemies in reach (like 3.x WWA) or made more than one attack roll (to some specific end) might be included, at-will multi-attacking is something that any maneuver-based alternative to the fighter would have to give up to open up design spaced to greater versatility.
Is it really that strange an idea? The Eldritch Knight already gives up its 4 attacks per round when it casts most of its spells. But few people seem concerned about the "conflict with design philosophy" there. Even the 7th/18th level features don't let an EK use all of its attacks when it casts. I'm just having a hard time seeing what's so different or game-breaking in my hypothetical suggestion. It'd just need a new "spell list".
Look, EKs can already do this in limited form by taking the cantrips "Green-flame Blade" or "Booming Blade"! And for a few levels it's actually somewhat worthwhile, if you have nothing better to do with your bonus action. Would it be so badwrong or hazardous to take the idea those spells present and run with it, making a much longer list with levels?
A fighter does get 4 attacks per turn at-will--at level 20, so it barely ever comes up. The level 11 feature (a third attack) is a far better comparison. A valor bard gets 4 attacks per turn at level 10 for a minute at a time when it casts Swift Quiver. Now, I know that's not an entirely fair comparison, as it eats the bonus action, uses a 5th level spell slot, restricts weapon choice, level 11 hand crossbow fighter with feats can do the same thing every turn, yada yada.
Edit: Forgot to finish this point. I was trying to point out that we already "dip" both ways, in giving other classes access to "extra attacks" in a limited form, and giving the fighter the option to give up its extra attacks to do something else. This kind of stuff is done in core. I'd be interested in taking the idea further.