What's interesting is that Tron is actually not THAT much shorter than Disneyland's Space Mountain-it's only about a difference of 300 feet in length, which isn't that much in the grand scheme of things. It's also only about 30 feet shorter than the shorter of the two tracks on WDW's Space Mountain.
But Tron FEELS much shorter for whatever reason. Perhaps because both Space Mountains wrap around many times within their structure and Tron is in much more expansive building, particularly compared to DL's. It's experientially hollow in comparison to either US Space Mountain, but people will eat it up because people like shiny, instagrammable things. Theoretically anyway-we'll have to see if Guardians works against its reception in Florida.
I'm guessing Pirates simply has to be the most popular ride in Shanghai for sheer capacity reasons alone.