When I have been at parks with people who have got whatever equivalent of Fast Track there has been, their measurement of the service has been based on how long their queue has been, not the Standby queue. I've walked through completely empty queues for many rides and people have still called the service great value because they themselves haven't had to queue.
Ergo, I believe many more people would complain if they knew the facts about these services. The worst thing by far for me is that it creates an immediate incentive for parks to reduce throughput (not saying Thorpe do this - don't hate me sassy THORPE PARK account).