If it weren't for the photo that Kyle has of Sarah in the first movie, I think it would've been a cool idea if John Connor was just some guy who rose to the occasion to fight Skynet. But when Kyle Reese was sent back in time he fathered another John Connor with a different Sarah Connor, and thus a new timeline is created where this John Connor is the resistance leader because of prior knowledge and training his whole life for Judgment Day.
Yea, I actually think Skynet screwed the pooch by sending back the first terminator because what they ended up with was a much better prepared John Connor in the altered timelines.
Look at the stuff that was happening in the glimpses we got of the future in the first movie. It definitely looked like Skynet was winning. To use a football analogy it's like Skynet kept handing off the ball at the end of the game looking to run up the score instead of just taking the kneel down to run out the clock.