With the slow exit, it's a 75 to 90-minute commitment for a decent seat. Which is way too long if you have a single night, and feels like a slog if you're used to zipping through 3 houses with Express in that amount of time. Best show in that venue not named "Bill & Teds," but I've only seen it once in 8 nights for that reason. (And even then it was because a friend backdoored me in.)
RHPS, arguably the most popular of the secondary shows, used the second-tier BJ seating maybe two nights that I saw. Nowhere near capacity. The magic shows are always sparse, largely because it's the same 25-minute set five times a night. Brian Brushwood changed it up and did TWO different shows, but with a repeat crowd, even that wasn't enough.
You make excellent points about capacity, as usual, and I don't think your point about non-IP houses is wrong. The normals are there for IPs, once they're tired don't really care about the originals. But I think the flaw in your thinking is that plenty of the lifestyler guests would rather hang in the streets than see a lame show.
I also don't buy the lighting in a bottle theory, big as this year's IPs are. HHN is having a moment, being embraced by the locals and regular out-of-towners Disney went out of its way to reject. Only two things will effectively cut the crowd:
- higher prices (tho maybe not as high as I've argued if the $90 difference between RoF and FF really made a difference)
- the Mouse finally following through with a Nightmare Before Christmas/Villain event in DHS.
Not to my recollection either, but feeling old today so I did a deep dive. No mention on the HHN wiki. IU doesn't go back that far, but no mention in the WDWMagic HHN 17 discussion thread, no mention from October 2017 on the DisBoards. Express sold out opening weekend -- and the #1 complaint was still the crowds -- but no mention of a FFP sell-out.