You might as well be comparing something like Vertigo to something like Die Hard... they're both masterpieces of their own genres. All you're really actually doing is just stating you have a preference for the action genre as opposed to, say, the drama thriller genre. I love all of those rides very much for very different reasons, but personally if I were forced to make the choice of destroying Pirates/Haunted Mansion or Spiderman/Forbidden Journey, I'd destroy the Universal choices in a heartbeat even though it would suck immensely to lose them. Attractions like Haunted Mansion and Pirates tap MUCH deeper into a collective consciousness of imagination, drawing upon very broad mythology that's embedded in our culture and crystallizes them into a perfect embodiment of those mythologies. In turn, they've had a huge influence on culture themselves. When you think about a haunted house or pirates in general, tell me your impressions of those haven't been colored by what you've experienced on those rides. Plus they are much more broadly accessible, physically and culturally. You've really had to have experienced the Harry Potter or Spiderman stories firsthand for those attractions to have their full effect, but everyone has an inherent knowledge of the idea of a haunted house or seafaring pirates.
Long story short, you just can't say Pirates/Mansion aren't great when compared to Spiderman/FJ/etc. Well, I take that back, you can say that, and you did, it's just not anything close to resembling a fact.
I think it could easily damn well could be. First off, there's a fair amount of evidence that the general public is unsatisfied with the lack of variety of types of attractions at Universal. People are a bit fatigued by the screen-based, height-restricted, thrill-oriented attractions that Universal has mostly been focusing on for nearly two decades now. People love attractions that are loaded with visceral details (just look at the average Joe soaking in Diagon Alley), and rides like the Haunted Mansion are jam-packed with them. To flip your hypothetical on its head, you can look to Disneyland in California for an inverse example: over the years they have added very successful thrill rides in the vein of Spiderman and Forbidden Journey in the form of Star Tours and the Indiana Jones Adventure, BUT they did not diminish the popularity of Mansion or Pirates whatsoever... they only increased the popularity of the park as a whole. Yes, Universal was trying to grab a particular audience for a while, but they are obviously trying to diversify now, as evidenced by Volcano Bay and Super Nintendo World. They're trying to grab as big a chunk of that family-friendly pie from Disney as they can.
In the case of E.T., unfortunately, I think it suffers from a variety of factors. First, the IP hasn't really stayed in the cultural zeitgeist the way something even like Back to the Future has. Second, they have not made any basic effort to keep it somewhat up-to-date, the way Disney has with new technology and effects on Mansion and Pirates. Third, I think it's in kind of a relatively dead area of the park. Considering all of that, though, I feel like it still actually commands respectable wait times on average.
