Think this topic comes up way too often.
As everyone has said before no one is going to work there butts off to put a local ahead of a foreigner (or vice versa) if that flight was clearly no 2.
The point why it might seem that the locals get preference is that there are more of those flights operating than other airlines. If a direct route becomes available it will be given etc however you might hear that different flights by the same airline all get offered direct routing and then maybe only one foreign airline but think of the numbers. there might only be 1 foreign airline in the airspace at that time as opposed to 5 or 6 locals so altough everyone is getting the same preferential treatment it sounds like its biased towards the locals cause there are more of them.