From 1981-82 to 1986-87 (6 seasons), Gretzky averaged:
203 points = 73 goals, 130 assists (+76)
In those 6 years, the next-best goal scorer (Bossy) had 105 fewer goals... and this was the guy many said then was the best goal-scorer ever.
In those 6 years, his assists are 337 more than 2nd-best Peter Stastny.
In those 6 years, his points are best by a 1219 to 698 (Bossy) margin -- nearly 2 to 1.
His plus/minus is best by a +456 to +279 (Kurri) margin. If you don't count his linemate and teammate (Coffey), that difference is +456 to +262, nearly +200 better than Hall of Fame D-man Mark Howe.
How about those 6 years' playoffs? His PPG is best by a 2.08 to 1.53 margin, but that 2nd-place is Barry Pederson's piddly 34 games and #3 is Wayne's linemate Jari Kurri. If you waive those two, Gretzky beats Rick Middleton by a 2.08 to 1.38 per-game margin. In the playoffs he went +28 in 18 games in 1985, scoring 7 goals in 5 games in the Finals against the League's toughest defensive team.
During those 6 years, Gretzky also won the Hart Trophy every year (actually 8 in a row), and his team finished 1st in its division every season, and 1st overall 3 times. He won the Stanley Cup 3 times in 4 years, and made the Finals 4 times (and won the Canada Cup, as leading scorer, twice in two tries). He led the NHL playoffs in scoring every time he made the Finals (x 4), setting all-time marks for assists and points and plus/minus that have never been matched.
As far as any 6 seasons go? Forget about it. Gretzky's 1981-82 through 1986-87 craps on every Hall of Famer ever.
Now, if you want to whittle seasons down to maybe 3, a case can be made for Bobby Orr's 1969-70 to 1971-72 (including both his Stanley Cups). I wouldn't make that argument, but you could. Or, if you want to inflate the seasons up to more than, say, 15, a case can be made for Gordie Howe. But any measure of player seasons larger than 3 and less than 16 is result-Gretzky. And no 6 seasons in NHL past or future matched/will match what he did during 1981-82 to 1986-87.