I agree they aren’t antithetical, but that extra work is pretense in a literal sense. You’re doing that extra work to present a more convincing illusion that the game mechanics represent real things. The underlying truth will always be that they’re just game mechanics though.
To be clear, I think that work is worth doing in a lot of cases, this one included. None of us would be here if we didn’t want our games to present the pretense of representing a consistent reality, we’d be playing… I don’t know, Yahtzee or something.
No, I think that's too glib. I mean, just rhetorically, it's a bad choice because it encourages this:
And it’s 2008 again and everyone is up in arms about presentation and not substance.
But more broadly, the function of each item in the game is different when you change the context. The design necessarily changes when you want an enemy to hit a target of 64 DPS, but a longsword does a specific thing; you decide to give them a different weapon, you come up with an alternate ability that modifies their damage, and so on and so on, and now suddenly hobgoblins (or gladiators or whatever piece of mechanical representation you pick) have an identity that continues when you're fighting a hobgoblin warlord or a frost giant gladiator later.
More importantly, the player can use both the rules and the fiction to draw conclusions about the functioning of the game world. The interesting bit isn't in "making up an explanation that makes the math work" but in the design constraints that your existing rules create; longswords are constrained to being a specific thing, and I can use that information as a player to make decisions about the world state.
Admittedly this doesn't matter a ton for monster attack values, it would be far more salient and interesting in a game with an explicated skill system. If climbing works a specific way, then I can infer how an NPC would have used it when I'm forensically tracking their break into a castle, or be alarmed when they scurry up a wall I can't touch, because of what that means about their stats.
It's not something you add to a set of existing mechanics, an additional mask on top of gameplay, it's much more about the ultimate design/gameplay loop impacts (in a real sense, about what freedom of design you've lost) as a result of those choices. "Pretense" suggests that it's a secondary design consideration, that the expected DPR of a CR 13 threat, the monster design from a business card, has (and should have) more ultimate design weight.