Maybe it's just me. But 5 sounds like a lot. Like a good number. I wish more theme parks had at least 5 dark rides.True, but to be fair IOA was meant to be the opposite of USF. And IOA's biggest current complaint is lack of things to do in the rain, and they have four dark rides. This might have five which is not much better.
How many does Animal Kingdom have? 2? And one of them is fairly new.
Hollywood Studios? 1? 2 if you count Tower of Terror I guess. (Until Mickey and Rise of course, but even then still only 3 or 4.)
Epcot has I think 5 if you count Test Track, and 3 of them are boat rides, one of which is through a greenhouse.
Even Magic Kingdom, which has the most rides ever, still only has 7 completely indoor dark rides.
I think 5 is great.
Could be worse. Could be SeaWorld with only 1, or Busch Gardens Tampa Bay with 0 lol.
(Wrote this fast, my apologies if I missed any.)