I never argued within that example that such would require changes to "class/role expression" beyond merely tanks being capable of more than mere meat-tanking DPS-play with an auxiliary sequence of CDs thrown atop (at this point, with no effect on anything else in one's play).
But let's be clear: it would require both. Difficulty makes the gameplay loops relevant, largely by preventing you from (timely) clears without partaking in that gameplay, but its the game, its code, and its engine, themselves, that determine whether those gameplay loops are even possible.
No matter how punishing you make it not to do something, you cannot suddenly do what the game's engine isn't capable of doing. XIV allows only for a very poor imitation of precision; if it wanted to make the adjacent gameplay relevant, it'd need to be capable of that gameplay. It's not. There's reason Asmongold, for instance, received only pained chuckles and moans when he attempted to dodge out of range of enemy strikes between his swings with anything less than Sprint and an 10-yalm headstart.