Luck would always be a factor, but the effects of "luck", or variance, should be greatly diminished over the long run. Ignoring all results and focusing on each individual situation at hand, doing the best to play "perfect" poker (which is practically impossible in NLHE), and coming closer and closer to that goal certainly has a much better chance of producing favorable results, but the game being as it is, even playing to the best of your ability you aren't always promised satisfying results. And by looking at the results, as the OP said, a bad player on a hot run may become complacent with a game filled with leaks, while a great player playing perfectly (just for example's sake) may still encounter a big downswing that will cloud his judgement on future decisions, perhaps even creating leaks in his previously perfect game.