As someone who rode both Wicked Witches Haunt and The Haunted House (very young mind). I believe the transit system on WWH was the same one used on The Spirit of London at Madame Tussauds. Even though it's 2 per carriage, the carriages are in constant movement and are linked all together. Whether or not that means WWH's throughput was higher I'm not entirely certain but I am inclined to believe that it did have a higher throughput than HH but HH wasn't a slouch either. I think that only time I ever queued for HH was my first time going to Alton Towers around late 90's. My mother and I were amazed with Emily Alton effect. One of my most potent memories of HH to be honest.