All the examples he used shared something in common most of the game's lifespan, they were endgame activities, they don't want matchmaking for endgame activities, they've said it thousand of times.
The absolute only thing that matters in terms of optional matchmaking is whether or not the activity needs communication or not. That should be the ONLY factor.
And activities like the Daily Story and Challenge of the Elders did not require communication at all. Non-Skolas Prison of Elders didn't either. You'll notice I'm being specific: matchmaking for the Skolas PoE would have been a mess.
You come off as if, "Well, Bungie said they don't want it. So I guess that's it and we should never question it and they know what they're talking about."
And despite you constantly ignoring the point when it's made, Nightfall almost never required communication either. It should have optional matchmaking. Simple as that.