Orrs primary responsibility was defense.
Gretzy was a Center where the puck is controlled.
Bobby Orr only lasted 12 season with about 7 of those seasons on a bad knee that only got worse because the other teams Thugs would go after him. Still Orr dominated. Still Orr holds the NHL record of scoring 100 points 6 times as a Defenseman.
Gretzy did not have to face the NHL GOAT team Montreal Canadians year after year. In the same division too.
66 Montreal Champs
67 Toronto Champs
68 Montreal Champs
69 Montreal Champs
70 Boston Champs
71 Montreal Champs
72 Boston Champs
73 Montreal Champs
74 Philadelphia Champs
75 Philadelphia Champs
76 Montreal Champs
77 Montreal Champs
78 Montreal Champs
8 times the Canadians won the Stanley Cup during Orrs tenure. Montreal reloaded with Hall of Famers like the NY Yankees year after year. Gretzys Edmonton team was full of Hall of Famers too - Messier, Anderson, Kurri, Coffey scored 100 points 5 times and is 2nd to Bobby Orr.
Orr did not have particularly great players around him. Orr out scored Center Phil Esposito as a defenseman.
This sums up Bobby "GOAT" Orr. A Bruins defenseman scoring the deciding winning goal in the Stanley Cup finals.