My opinion based on what you have written is that yes, the heeler accepts your leadership, the GSD does not. He thinks its "his job" to protect the pack from what he deems as an intruder (the heeler). Your GSD is about 1.5 years old, he's maturing, and trying to climb up the totem pole. Not unexpected at all.
If you know what you're doing when it comes to obedience training, just get them out in a strange place (a field of some sort) and work them in heeling/downing/sitting, whatever other obedience exercises you might be interested in. I would consider getting a trainer that could show you how to properly handle your dog and maybe give you a goal to work towards something.
Really just sounds like a growing/maturing boy trying to find his place in the pack.
CD RE TC HIC 7/10