More quests then more dungs. And far as I know its easier to make "Talk to this NPC" he gives you this shit, bring this shit to "This NPC" , now yo must bla bla.
Dungs require more work far as I know. But if there are maps ready and they just need concept, whats so hard about it ?
Damaged BoS outpost, find some item bla bla, or just loot it
Supermarket with basement, big place, nice loot, several entrances/exists etc.
I really don't see a problem, but probably devs don't have time to add all this during 1 year/session, so I'm sure in about 5 years we will have some decent loner playability.