Are you sure? I think that, at their peaks, the latter 4 probably had a greater percentage gap in adjusted assists than the former 4 had in adjusted goals, if you take each player's 3 best seasons.
I'm not trying to say goals always > assists. In the case of elite playmakers (you know who they are, they drive the offense all the way, they just don't take the shot) assists are worth as much as goals. But for most players they aren't.
adjusted goals:
Bure 65,64,59 = 188 goals
Selanne 62, 60, 54 = 176 goals
Kariya 48, 46,46 = 140 goals
Neely 46, 46, 45 = 137 goals
Crosby 56,39,38 = 133 goals
Malkin 52,37,35 = 124 goals
Thornton 41,40,32 = 113 goals
Forsberg 34,33,29 = 96 goals
adjusted assists:
Thornton 92, 92, 73 = 257 assists
Forsberg 85, 83, 76 = 244 assists
Crosby 84, 71, 61 = 216 assists
Malkin 80, 63, 52 = 195 assists
Selanne 68, 65, 60 = 193 assists
Kariya 70, 62, 57 = 189 assists
Bure 45,43,40 = 128 assists
Neely 35,31,31 = 97 assists
Selanne
Thornton has 33.2% more assists than Selanne
Selanne has 55.8% more goals than Thornton
Forsberg has 26.4% more assists than Selanne
Selanne has 83.3% more goals than Forsberg
Crosby has 11.9% more assists than Selanne
Selanne has 32.3% more goals than Crosby
Malkin has 1.0% more assists than Selanne
Selanne has 41.9% more goals than Malkin
Selanne wins 4 and loses 0
Bure
Thornton has 100.08% more assists than Bure
Bure has 66.4% more goals than Thornton
Forsberg has 90.6% more assists than Bure
Bure has 95.8% more goals than Forsberg
Crosby has 68.8% more assists than Bure
Bure has 41.4% more goals than Crosby
Malkin has 52.3% more assists than Bure
Bure has 51.6% more goals than Malkin
Bure wins 1 and loses 3
Kariya
Thornton has 36% more assists than Kariya
Kariya has 23.9% more goals than Thornton
Forsberg has 29.1% more assists than Kariya
Kariya has 45.8% more goals than Forsberg
Crosby has 14.3% more assists than Kariya
Kariya has 5.3% more goals than Crosby
Malkin has 3.2% more assists than Kariya
Kariya has 12.9% more goals than Malkin
Kariya wins 2 and loses 2
Neely
Thornton has 165% more assists than Neely
Neely has 21.2% more goals than Thornton
Forsberg has 152% more assists than Neely
Neely has 42.7% more goals than Forsberg
Crosby has 122.7% more assists than Neely
Neely has 3% more goals than Crosby
Malkin has 101% more assists than Neely
Neely has 10.5% more goals than Malkin
Neely wins 0 and loses 4
Head to head wins:
Selanne 4
Thornton 3
Crosby 3
Malkin 2
Kariya 2
Bure 1
Forsberg 1