But Luke doesn't hit the exhaust port because of one of his "gunner" skills, he hits it because of he is powerful in the force. Turning off his targeting computer, remember?
That's conjecture and not exclusive of the need to have "Exhaust Port." Obi-Wan's lesson to "Let go" - was an extension of his "act on instinct" lesson earlier. Mechanically, it could be said that what Luke did was give himself a boost through "Touch of Fate" to add two blue - probably not by itself enough to overcome Massive 10. Other pilots probably had "Exhaust Port" as well, but that wasn't enough, because they needed the better chance afforded by "Touch of Fate." It's possible, that as a targeting array upgrades a die, Luke was already upgraded as far as he could be, and thus would receive no benefit. Instead, by using "Touch of Fate" he was able to increase his pool size and thus achieve the needed successes.
I would also think that he flipped a Destiny Point to achieve that, in addition to everything else.
This topic is definitely interesting, let's go on and build Luke Skaywalker in episode 5 too, it will be most interesting.