Thor being on a higher level in many respects is part of what makes this a great rivalry when it is well handled (which it hasn't been in years, but that is a separate issue).
I know as Thor fans, we tend to get defensive, and there are good reasons for that. Thor has been treated like a chump way too many times in recent years.
That said, Hulk and Thor having a rivalry and putting each other to the test in the strength department doesn't take anything away from Thor, to the extent that it is handled properly.
I agree that Thor fighting Hulk should not be the standard state of affairs, only an occasional thing that happens in exceptional circumstances. But when it does happen, it should be a great fight that gives fans of both characters something to cheer about.
In the interest of full disclosure, I wouldn't mind seeing Thor give Hulk a royal butt-whooping sometime soon, but that is only to balance the scales a bit, since Thor has been on the receiving end so often in recent years