It's not only the car. I don't like Hamilton, but he rarely ever makes silly mistakes, unlike Vettel. He's sitting in the better car, yes, but he's also the better driver. Silly mistakes aside, Vettel doesn't seem capable of getting 100% out of his car, like someone like prime Alonso could.
Btw. Vettel too has had his fair share of luck by sitting in a red bull cockpit at the right time.