My only real comment is if you come at mid-day, technically the parks busiest time, then inevitably you will see queues at the highest they are going to be. I also get the feeling that if you were walking round the park avoiding queues because of the wait then, yeah, you aren't going to get on much. I'm not sure what other rides you went on as your trip report only mentions Slammer, Colossus and Stealth (albeit, both front rows which makes up for lack of other rides) but if you had gone on things like Fish, Storm in a Teacup, Quantum, No Way Out then you would have got on far more..