I get the point you are making, but it doesn’t really scale as much as you think. Let’s say a popular ride has a 30 minute wait. In your example the ride loads 1000 guests and hour. So that is 500 people in line. If the ride is 1 minute long, that means about 17 people are on the ride at any given time. If the ride is 15 minutes long, that’s 250 people on the ride. Yes, that’s 15x the capacity, but the longer ride is only increasing total capacity by about 233 people. The line is actually the bigger people eater.
Logistically, you want to build a ride the will create the longest line people are willing to stand in. Tron will likely draw more people then Journey of the Little Mermaid.
The impact of ride length on customer satisfaction is a completely different analysis, but your point was about capacity.
So, while we would all love a dark ride with high capacity and well executed story that lasted for 10+ minutes, I doubt we will see the likes of that again, because Disney can’t afford to build a ride where people get board, because then you end up with no line. Instead, we now get “interactive” or story telling cues. They become part of the experience. It not a 30 minute line and 1 minute ride, it’s a 31 minute experience!