Needed might be the wrong word, but your words imply that mechanics are combat-centric. Your words:
"As long as the game rules are disproportionately focused on resolving combat, discussion of the game’s design will be similarly focused on combat. Obviously DMs can compensate for this combat focus on their own tables, but we’re talking about the game’s design and mechanics here."
So I point out that skill checks are just as important as combat, and they are also intricate to the mechanics of the game. I mean, stealth is just as strong as a good armor class. The ability to nature check a creature could increase damage as much as a barbarian going into rage. So skills count. Yet, they are avoided in the discussion, because it is not a number added to a person's to hit, damage or spell dc. I find that to be a limited take, and not addressing the debate in its entirety.