Even when there was an instance reservation time, declining instances still hurts yourself a lot too. Let's say it takes 5 minutes to reserve an instance and 30 minutes to clear WP. Do you really think you'll get a 2/3 WP in 6 tries? I find it hard to believe a tank can get a 2/3 WP in 6 tries given there's really no incentive for a tank to leave at 2/3, so you still end up spending more time than just taking the first available spot. In the end, everyone loses, and the guy trying to cheat the system most likely loses the most because he has to fight all the other guys who are trying to cheat the system too.