Right, it’s both.
I don’t think people want a challenge that isn’t challenging. I think that’s true of almost everyone.
That’s the benefit to it being open world. In that the world is a place where you can put challenging (not mythic but maybe LFR > norm > heroic tiers) embedded within the open world dungeon / raid. Players will flock to this content for upgrades and will do what’s necessary to get them. Including finding other people.
And the way the encounters would be designed would favor numbers over mechanics. You’d still have mechanics but the idea would be that more is always better.
That’s how the open world should be.