There's no doubt Lemieux was (duh!) far and away the best Penguin during 1984 to 1989/90-ish, and after that was only the best Penguin by a somewhat smaller degree. Still, this line of "so-and-so was totally alone" never really holds up to close scrutiny, I think. I mean, these are NHL players. They were among the best players in the world if they were allowed to go out on the power-play for an NHL team. Rob Brown, I believe, outscored Theo Fleury in Junior. Quinn was quite a good player for several years. Paul Coffey (from 11.1987) a Hall of Famer.
I was watching highlights of a Pens game from 1984-85 (Lemieux's rookie year) the other day, and in the game Mario had a good night with 2 goals. But what was surprising was that his 2 goals were rather easy, and both were set up by Warren Young, who did the grudge work. I mean, the conventional thinking is that "scorin' Warren" was a bit of a plug whose stats were elevated by playing with Mario for a year or two. There's some truth to that, of course, but as this game demonstrated, even Warren Young could be the guy who helped Lemieux score some of his points.
Not to put too fine a point on it, because Lemieux did totally dominate his team's offense c.1985 to 1988 by huge degrees, but the Pens were not an offensively poor team. (In fact, didn't the '88 or '89 Pens have the 2nd-most 20-goal scorers in NHL history or something like that?)