Actually, John is the most known quantity of all time in ficton: the Destined Hero Coming of Age. Go grab 3 books off the SFF racks and he'll be in two of them. The only thing that sets him apart is the moral quandary of what he did to his father, not only for what I said before, but also because it raises the question of whether or not he was ensuring his own survival. Without that, he's fiction's most generic character. The entire point was to see the archetype through the eyes of his mother. Without that element, when Sarah's part of the story is done, it blends in with everything else.

Skynet's goal was advancing science. They just lost control of their experiment. The "evil" Skynet isn't the creators, it's the machines. The machines, I've always assumed, are independent thought contrasting with programming.

The "self-fulfilling prophecy" is what makes the mytharc interesting. Did John know how the chip got there in the first place, or was he naive about that until later? Would it have happened anyway, just at a slower pace? If Sarah hadn't gone around blowing up things she thought would lead to machines taking over the world? If she'd lived quietly in hiding, would they have ever known how to find her?