Why do you think it's myopic?
Because, as I have repeatedly stated, you are ignoring any way that something might matter in a game OTHER than ways which are directly related to metagame concepts like challenge levels and the DM's previous plans.
You acknowledge, in our given suggestion, ONLY the numerical challenge rating of the encounter as "meaningful." Any other change to the encounter, to the gameplay experience, or to the plot of the game, you discard as not being meaningful.
That's myopic.
The best explanation I can come up with is that you really do believe that D&D is some sort of war between the PCs and the module. I mean, really, you probably don't believe that, but its the only view of the game that makes your position make sense. From that point of view, there is some kind of objective reality that exists apart from the DMs decisions and the player's experience of the game. A pre existing, "correct" world. And if the PCs come up with an unusual way to defeat the module, and the DM adjusts the module to be more difficult to counter that unusual plan, the DM has somehow "cheated" the players. He's altered the "real" way the adventure is "supposed" to work, and he's done to so to negate the PCs decisions.
But that point of view isn't how D&D is really experienced. Its NOT a war between players and a module. There is no "real" world in which the PCs operate, there's an imaginary one that exists as a sort of shared fantasy between the players and the DM. The module might inform it, but it isn't the actual world. The same is true of the DMs intentions before they hit the game table. If a DM intends one thing, then changes his mind because of a player's decision, he's not cheating. He's not rendering a decision meaningless.
That's why I find some of your positions so baffling. You've literally taken the position that a DM who plans one encounter then changes it could be rendering someone's decision meaningless, but a DM who doesn't plan at all and simply creates the latter encounter to start with isn't rendering anyone's decisions meaningless.
I mean, seriously, you really want to take the position that, if a player elects to have his character train in Stealth instead of Intimidate, that you've rendered his decision meaningless if instead of a scenario where he needs to intimidate a guard you put in a scenario where he needs to sneak past a guard? Because that's a really, really myopic view. It only takes into account win/loss chances and final outcomes of the encounter, and completely neglects the experience while the character is IN the encounter.
I think the weirdest part of all of this, is that if you really stop and think about it, you've come up with a theoretical framework that lets the players metagame and use their metagame insights to accuse the DM of metagaming.
That's his job.