Well let's say i build a old timer tracked ride in the park, no matter how i design it, it always have queues up to 66 minutes due to the issue of the loading and unloading of passengers.
Same goes out to the go karts, the Water rides. The coasters i am agree on have a good capacity on their own, but the loading could be more efficient. The main issue of the loading is in the trackedrides. The only solution is a double loading station, but then the cars you can put on the track are limited.
But for the coasters, the long queues are not a result of the boarding process. It has more to do with you letting to many guests in your park, or most likely: unbalance in the AI system.