Crunch all the numbers you want but there's no comparison to the Studio Tour at Disneyland. Nothing will keep guests on a ride for 45 minutes at DLR (barring a breakdown). Considering some of the ride times, that's anywhere from 5 to 10 attractions in DL. It's just a different beast altogether.
And while the attendance maybe lower than Universal's expectations, Universal did this. They jacked up the gate price AND introduced dynamic pricing AND restructured their APs and added more blackout dates, etc. They made it so people have way less access to the park for less than the price of a 1-day ticket, and for an attraction that's been in FL for six years.
But WWOHP isn't an important addition to Universal's parks because it increases attendance. Pretty much every new attraction at any theme park does that. It changed how guests consume a themed land in terms of shopping, food, and beverage. I'm sure Universal might prefer less people in 120+ minute lines and more buying $50 wands, $100 robes, and drinking $6 Butterbeers (I'm guesstimating). They will come away with similar dividends and probably much higher guest satisfaction.
Remember, this is the same land that made Disney reevaluate how they create theme park lands and its influence, which already can be seen in Cars Land, and will continue in the development of Star Wars land, is helping to keep burgers and chicken nuggets out of restaurants and DisneyParks sweatshirts out of stores.
