John's quite competent with a gun and knows how to handle himself in a fight. We've gotten plenty of evidence of that. So Sarah's trained him well in that regard. But the guy who's going reprogram machines, organize time travel missions and direct a battle against a technological enemy isn't a badass soldier, he's essentially a badass nerd. And that's where I think Sarah has encouraged John's leadership. That's where she steps back and defaults to him.

The story we know of John isn't that he's this great leader when judgement day happens, it's that he becomes a leader when the human race had essentially given up and nearly become extinct. And we know he spend 6 years in a Skynet prison camp before he leads the revolt. Sarah's been his sole role model for most of his life and we've seen her drive and determination. So when the time finally comes (if they don't stop Skynet), I have absolutely no doubt that John will find that same strength within himself to become the man Kyle would die for.

Sarah wishes John could have a normal life and that's why she's been trying to change his fate. But you can't fault her for the kind of life they have to live ("we didn't choose this life, John, it chose us"). Maybe it does explain why John turns to Cameron, but that's a matter of their circumstance, not Sarah's choice.