The argument for Lemieux over Gretzky, in a nutshell:
1) The eye test. At one point in my life, I would have told you that Lemieux was a better hockey player than Gretzky. He just looked THAT good, on an aesthetic level in my mind with Muhammad Ali, Pele and Barry Sanders as jaw-droppingly, sublimely talented athletes who simply did whatever the hell they wanted against world-class competition. Grace and power in motion, at a level that maybe Bobby Orr could match.
2) The "what-if?" game. I think we've all been around this block a few times already. Gretzky played on a dynasty during his youth, while Lemieux basically carried the Pens on his back and won Cups as soon as they gave him something to work with. Lemieux made Kevin Stevens and Rob Brown into 50-goal scorers. Lemieux was passing to Brown when he reached the 200-point range, whereas Gretzky was passing to Kurri. What happens to those point totals if they swap wingers? Also, Lemieux's longevity was severely affected by injury and by cancer -- considering he came back and dominated at age 40, is it really fair to say he had less staying power than Gretzky?
3) The "Gretzky is overrated" angle. Wayne was the ultimate right-place-right-time story, as the playmaking center on a firewagon team during the highest-scoring period in history. Several of his teammates went on to Hall of Fame careers, and would have done so regardless whether they played with Wayne or not. Had he played primarily in the 1990s, when goalies were larger and more fundamentally sound, and opposing teams were far more willing to take liberties with slightly-built superstars, perhaps Gretzky's numbers come back down to earth a bit. Lemieux certainly never showed a lack of ability to score at will on 1990s goalies and to fight through 1990s obstruction, but Gretzky looked a bit less impressive as time wore on. It's common to hear from fans who were young in the 1990s that they were astonished by Lemieux and underwhelmed by Gretzky.
What the argument boils down to is that Lemieux was simply a better player than Gretzky, a force of nature that went largely to waste due to not being in the right time and place. That if you were drafting a team to win it all, you would be well served to take Mario #1.
^ I hope I represented that argument accurately. I think all the major points are in there.
I realize you aren't actually saying Lemieux was better, just summarizing the usual arguments. But I'll try to refute them anyways:
1. No argument. Lemieux looked better. That's actually what 90% of the debate comes down to, when you really get past the rhetoric.
2. Gretzky's first 200 pt season (212 pts, 92 goals) he spent most the year playing with Dave Semenko and Dave Lumley, not Kurri. I'd say Gretzky had no advantage that year in linemates, and put up more goals, assists, and points than Lemieux did at any point in his career. Lemieux also had time later with Jagr (not usually same line, but they were sometimes, and were together regularly on PP) and couldn't beat his own 199 pt season, let alone Gretzky's 215. Not saying Lemieux couldn't have done better with a better team, but this board has shown many times that linemates don't affect generational talents as much as generational talents affect their linemates.
3. Lemieux also looked better in the 90's because he was younger and played on a better team by then. If we are going to use Lemieux's poor team as a bonus for him at the start of his career, it seems strange to then not factor in that he was on a much better team in the 90's. He also played way less hockey, and Gretzky suffered a major injury in 91. Agreed that Gretzky's scoring was already dropping, but the "what if" game shouldn't only apply to Mario.
There is no denying that Gretzky's numbers were in a slow decline before the Suter hit, then plunged after it. It accelerated what should have been a slow decline into a much more rapid one. I do agree that Lemieux seemed better at an advanced age, but he also played the equivalent of 7 less seasons of hockey. He also took much longer to hit his stride than Gretzky did, who in his 2nd season broke records for most assists and points in a season, and in his 3rd broke both those records again, + goals as well. By his 3rd season he had broken every major scoring record there is. Lemieux never really came close (Gretzky is 1-4th in scoring, 1 & 2nd in most goals in a season, and 1-7th and then tied with Lemieux at 8th in assists. Even if we take out Gretzky's best seasons for each, he still holds every record.) Point is, while Lemieux may have been better late in their careers, he was not as good early in their respective careers. I'd say it balances out, except that Lemieux missed so much time late in his career that even this is probably not in his favor.
Gretzky was also better in the post season. Combined with longevity, his statistical dominance, his dominance in awards (yes, trophy counting isn't always accurate, but when it's that lopsided it has to mean something), and he even dominated in head to head matchups (even after leaving Edmonton). The points in favor of Lemieux usually require one to prorate stats for Lemieux only, ignore injuries for Lemieux only, and give unreasonable weight to the last 5 years of their careers, rather than what each accomplished during the span of their careers.
As someone else mentioned, if Lemieux were truly better, it should have shown up somewhere in the stats. The truth is, he just looks better on youtube. But so does Kovalchuk, and he's not better than Gretzky either.