It wasn't a gamist argument, though. It was a narrativist one. (The gamist argument would be about how mechanical design is needlessly laborious if things which serve different functions are forced to always use identical components; you wouldn't design an engine and a sprinkler system using 100% identical components.)
The narrativist argument is that the intended experience of playing the game, and the role within that experience that specific components play, needs to actually...serve that experience. It needs to make the experience satisfying and rewarding in and of itself. It's the same source as things like Chekhov's Gun. I even expressly said "an unsatisfying 'narrative', if you will" for a reason; this argument is about the story, the play-feel, the thematics of the experience.
Gamist arguments are about the mechanics themselves. We use the unrealistic to-hit and AC mechanics because actually modeling the real physical process of attacking a target in melee combat would be horrendously tedious while adding effectively nothing at all to the actual process. (See, for instance, the tedium of 3e's grapple rules.) That's a gamist argument. Conversely, a narrativist argument might be that we have classes because there is a more engaging story to be gained from making clear, measurable progress toward ultimate mastery, than there is in tiny incremental gains that only slowly coalesce into something better or stronger, even though the latter is much more like how people actually learn and develop.