SWH, you are completely mistaken.
ATC here is not the best but has certainly, in my time over the last 5 years here, improved markedly. They have an arrivals coordinator who may well try and slot an SIA ahead of you, but they are looking bigger picture to the overall arrival timings. If he is 30 mins late, they will try and expedite him to make the schedule closer.
If you are early, likewise you can expect to be slowed down/vectored to allow others who are late to make up the schedule