I think that Gretzky's goal-scoring arc was rather standard. He peaked between ages 21 and 24 (that is, 84/85 was his last peak season in terms of goal-scoring). He won his last goal-scoring title at the age of 26 (62 goals in 1986/87, which was already a far cry from his peak production of 92 and 87 goals).
In the three seasons before the Suter hit, Gretzky scored 40, 54, 40 goals.
In the three full seasons after and including the Suter hit, he scored 41, 31, 38 goals.
It is not like Suter brought Gretzky from his 70-80 goals form to less than 40-goal form. Gretzky already was averaging 45 goals in the three years before the hit vs. 81-goal average in his peak four years. And the hit allegedly pushed Gretzky down to 37 goals per season average. That's 20% decline after crossing the 30-years-old mark, that's rather normal and graceful aging.
The big decline was going from 81-goal average in 1981-85 to 45-goal average in 1987-90. That's a crash, that's losing nearly half of his goal-scoring production. But Gretzky is far from the only one - Brett Hull followed the same arc, Esposito, though a late bloomer, followed the same arc. Stamkos, Jagr, Selanne, Lafleur had similar declines from peak goal-scoring.
Only four goal-scorers in history were able to defy age and stay close to peak goal-scoring into their 30s: Richard, Howe, Bobby Hull, Ovechkin.