I dont know if slashing is the right word, but in my experience there over the summer, this was true to some extent. Diagon definitely did well but it was at the expense of some of the other areas in the park. In the exact words of my supervisor "it's not a flop by any means but it wasn't as crazy successful as they thought it would be."
Anyway, this is pretty neat...Im not a shareholder at Universal or anything but it's great that their expansions are paying off, and that gives them no reason to slow down in the future.