I agree with your disagreement. If the goal is just to make an extended film around a single idea, then yes it has a high likelihood of burning out after 10-20

I agree with your disagreement. If the goal is just to make an extended film around a single idea, then yes it has a high likelihood of burning out after 10-20 hours. If the goal is to set up a world that can act as a vehicle for commentary on the real world as it develops, then the only limiting factor is how long folks want to continue working on the show, as long as the audience is there. It's perfectly fine for something like a sitcom or sketch comedy show to have both long plot arcs as well as topical treatment of current events. And of course new storylines can be thought up over the course of a few years, as well as individual episodes that take creative detours. Also we have to remember that until very recently, series were consumed one episode at a time, in day/week intervals, or even longer. This I think also added to the deep emotional experience you mention for long-running series: we've lost the anticipation factor, and as the cliché goes, the anticipation of something is often better than the thing itself. It was like this for decades; Netflix streaming was introduced only about 13 years ago, it's first in-house series, House of Cards, came out 7 years ago. I think it'll still take a while for the industry–both creatively and logistically–to catch up to the cultural change we've undergone with binge watching streaming series.