Also take into account that it is an upcharge requirement meaning a bit less demand and is a circular attraction, but, an attraction on it's own. It seems that what is wanted here is an entrance to the land that is connected directly to the land and what you are about to see. Harry potter land is accessible from either park, but not from either park on the train unless additional payment is made. That alone would limit ridership. So, if you want the Star Wars thing to work it has to be an upcharge to be compared to Hogwarts because without the additional cost... Hogwarts doesn't exist. However, without the connection to SWL, Star Tours can exist on it's own, with no additional charge or become a completely new, unrelated adventure for everyone to use.When talking about capacity, I meant it as a "per hour" distinction, which is what's relevant here.
Hogwarts Express uses two 168 passenger trains for a total Cycle capacity of 336. The ride is ~4 minutes, and I would expect with load and unload that the actual cycle time is closer to 7 minutes. That's 2880 guests per hour total (so 1440 per leg). Admittedly these are estimates but it should at least put things in perspective.
Star Tours has six 40 passenger bays for a total Cycle capacity of 240. The ride is ~4.5 minutes and I would expect with load and unload that the actual cycle time is closer to 7.5 minutes. That's 1800 guests per hour total.