Do you notice a little bit of ontological reversal here? You're right that fluff is not rules, but fluff is the reason that the rules exist in the state that they do. WotC didn't collect together a random assortment of class features and then, only after the fact, decide to fluff that class as an quasi-Shaolin monk. They took the concept of a quasi-Shaolin monk and wrote the crunch to fit that concept. If instead you use crunch to determine fluff, well, hats off to you if you manage it, but isn't it kind of doing things the hard way? If a player comes to me and says she wants to play a martial artist who isn't a quasi-Shaolin monk, I'm inclined to just modify the class features to fit her concept, rather than make her come up with an explanation for why her character can speak every language and doesn't age when those abilities do nothing to advance the concept.
No. The designers create class features to cover as many character concepts as possible. There is no rule or intent to limit PCs with monk levels to Shaolin type concepts.
Uh... take another look at the battlemaster's Know Your Enemy feature.
Okay.
You may use this ability to tell if the target is your equal, superior or inferior in certain characteristics-game mechanics. For example, whether he is stronger or weaker than you.
This does not mean that the character knows about the game mechanics of Strength scores, even though the player does. Having this class feature doesn't mean that he becomes aware of game mechanics directly, only their effects in game, like 'stronger than me'.
Even the abilities which talk about specific game mechanics don't mean the
character knows about game mechanics. When the player compares AC, the in game effects of AC represent how difficult it is to hit and damage a creature. When the
player knows that the target has a lower AC, the
character knows that the target is easier to hit.
When the
player knows the target has more total levels than he, the
character feels that this guy is powerful, not that 'this guy must be at least 12th level', because characters are not aware of game mechanics.
Even the ability to know if the target has more or fewer fighter levels is a game mechanic that the player knows while the character only knows that the target has learned more or less than him in the specific kind of tricks in his field. It's like a classically trained french chef could work out whether or not another chef was classically trained, even though he knows that french cooking is not the only kind of cooking.
Although characters can know nothing of game mechanics, they
can know things that approximate them in the game world. For example, our characters cannot know what number came up on the d20, nor can they know that the BBEG has a +11 attack bonus; the
players can know these things. But the
characters can certainly be in combat and sooner or later work out how skillful the opponents are.
This is why attack rolls should be made in the open (as long as the attacker can be seen). For example, if the DM rolls a 3 and says 'hit', then you know, as a player, that the guy must have a great attack bonus. If the DM rolls a 17 and says 'miss', then these guys must be rubbish! But if the DM rolls 19 and says 'hit' or rolls 2 and says 'miss', you haven't learned much. As combat goes on, you may very well work out the guy's exact AC and attack modifier.
This is okay, not because the character knows what the player knows (game mechanics and die rolls) but because the character has his own way of judging how good the enemy is: by engaging them in combat.
The advantage the battlemaster has is that he is so observant that he can work this stuff out by watching someone when they're not even in combat! It still doesn't mean that battlemasters are aware of D&D game mechanics!