There is no case for Lemieux as the greatest of all time, no.
Mario was probably the best individual physical specimen of a hockey player that combined uber-elite skill, speed, size, and IQ. However, hockey is not played by individuals.
The best player of all time is the one who elevates his teammates the most while also distancing himself from competition by the highest of degrees, and does it consistently for many years in a row.
As far as the 'Big Four' go, I would probably rate them like this:
PEAK
1) Gretzky 1981 to 1986
2) Orr 1969 to 1972
3) Lemieux 1987 to 1993
4) Howe 1950 to 1954
PRIME
1) Gretzky 1979 to 1991
2) Orr 1968 to 1975
3A) Lemieux 1985 to 1996
3B) Howe 1949 to 1969
CONSISTENCY DURING PRIME YEARS
1) Gretzky
2) Orr
3) Howe
4) Lemieux
LENGTH OF PRIME YEARS
1) Howe
2A) Gretzky
2B) Lemieux
4) Orr
POSITIVE IMPACT ON TEAMMATES
1) Gretzky
2) Orr
3A) Howe
3B) Lemieux
If you were to look at the "winning" results here (more of a team accomplishment), I think Gretzky would have to win again, with four Cups (six Finals), all as leading scorer, and three Canada Cups, all as leading scorer. I guess Howe would be second, with Orr and Lemieux tied for third?
Anyway, the one stain on Gretzky's rule here is his October 1991 to April 1999 career, which is largely unimportant to his legacy (would have been different if not for McSorley's illegal stick). He played about 7.5 years past his prime, which is far longer than Howe (2 years maybe, before 1971 retirement), Orr (pretty much retired still in prime), Lemieux (several years after prime, but only about three-four seasons worth of play) did.
I also think Lemieux is the #1 goal-scorer in hockey history, with apologies to Ovechkin.
Lemieux’s case is mainly aesthetic. Watching the guy play, even in retrospect, I couldn’t imagine anyone else doing the things he did. Sometimes it really did feel like he was on another plane than the opponents, which is sometime people also said about Bobby Orr.
It’s almost a “you had to be there and see it for yourself” kind of thing. It’s really hard to quantify the experience of watching someone casually toying with the best players in the world.
This is true, but how many games were there in Mario's prime where he was "casually toying with the best players in the world" vs. games where he wasn't a big factor? That is, which of these guys showed up and made a difference the most games out of the season, year after year?