Well, let's compare them:
We can do 2, 3, 4, 5, 6, 7 years then.
2 Years:
[TABLE=collapse]
[TR]
[TD][/TD]
[TD]GP[/TD]
[TD]G[/TD]
[TD]A[/TD]
[TD]Pts[/TD]
[TD]Even Strength Points[/TD]
[TD]Hits[/TD]
[TD]Blocked Shots[/TD]
[TD]Awards Won[/TD]
[TD]Awards Nominated[/TD]
[/TR]
[TR]
[TD]Matthews[/TD]
[TD]147[/TD]
[TD]100[/TD]
[TD]91[/TD]
[TD]191[/TD]
[TD]134[/TD]
[TD]145[/TD]
[TD]154[/TD]
[TD]1All Star, Hart, Pearson, Richard[/TD]
[TD]Byng : 10; Selke: 10[/TD]
[/TR]
[TR]
[TD]Mackinnon[/TD]
[TD]136[/TD]
[TD]74[/TD]
[TD]125[/TD]
[TD]199[/TD]
[TD]138[/TD]
[TD]121[/TD]
[TD]79[/TD]
[TD][/TD]
[TD]6th All Star; Byng: 66[/TD]
[/TR]
[/TABLE]
3 Years:
[TABLE=collapse]
[TR]
[TD][/TD]
[TD]GP[/TD]
[TD]A[/TD]
[TD]A[/TD]
[TD]Pts[/TD]
[TD]Even Strength Points[/TD]
[TD]Hits[/TD]
[TD]Blocked Shots[/TD]
[TD]Awards Won[/TD]
[TD]Awards Nominated[/TD]
[/TR]
[TR]
[TD]Matthews[/TD]
[TD]199[/TD]
[TD]141[/TD]
[TD]116[/TD]
[TD]257[/TD]
[TD]187[/TD]
[TD]202[/TD]
[TD]201[/TD]
[TD]All Star: 1
All Star: 2
Hart
Pearson
Richard
Richard[/TD]
[TD]Hart: 2
Byng: 3, 10
Selke: 10, 27[/TD]
[/TR]
[TR]
[TD]Mackinnon[/TD]
[TD]184[/TD]
[TD]94[/TD]
[TD]170[/TD]
[TD]264[/TD]
[TD]178[/TD]
[TD]159[/TD]
[TD]94[/TD]
[TD][/TD]
[TD]Hart: 3
Selke: 22
Byng: 11, 66
All Star: 3, 6[/TD]
[/TR]
[/TABLE]
4 Years:
[TABLE=collapse]
[TR]
[TD][/TD]
[TD]GP[/TD]
[TD]G[/TD]
[TD]A[/TD]
[TD]Pts[/TD]
[TD]Even Strength Points[/TD]
[TD]Hits[/TD]
[TD]Blocked Shots[/TD]
[TD]Awards Won[/TD]
[TD]Awards Nominated[/TD]
[/TR]
[TR]
[TD]Matthews[/TD]
[TD]269[/TD]
[TD]188[/TD]
[TD]149[/TD]
[TD]337[/TD]
[TD]242[/TD]
[TD]242[/TD]
[TD]261[/TD]
[TD]All Star: 1
All Star: 2
Hart
Pearson
Richard
Richard[/TD]
[TD]Hart: 2, 10
Byng: 2, 3, 10
Selke: 10, 16, 27
All Star: 4[/TD]
[/TR]
[TR]
[TD]Mackinnon[/TD]
[TD]253[/TD]
[TD]129[/TD]
[TD]228[/TD]
[TD]357[/TD]
[TD]240[/TD]
[TD]210[/TD]
[TD]125[/TD]
[TD]Byng
All Star: 2[/TD]
[TD]Hart: 2, 3
Selke: 22, 26
Byng: 11, 66
All Star: 3, 6[/TD]
[/TR]
[/TABLE]
5 Years:
[TABLE=collapse]
[TR]
[TD][/TD]
[TD]GP[/TD]
[TD]G[/TD]
[TD]A[/TD]
[TD]Pts[/TD]
[TD]Even Strength Points[/TD]
[TD]Hits[/TD]
[TD]Blocked Shots[/TD]
[TD]Awards Won[/TD]
[TD]Awards Nominated[/TD]
[/TR]
[TR]
[TD]Matthews[/TD]
[TD]337[/TD]
[TD]225[/TD]
[TD]185[/TD]
[TD]410[/TD]
[TD]295[/TD]
[TD]270[/TD]
[TD]321[/TD]
[TD]All Star: 1
All Star: 2
Hart
Pearson
Richard
Richard[/TD]
[TD]Hart: 2, 10
Byng: 2, 3, 8, 10
Selke: 10, 16, 27
All Star: 4[/TD]
[/TR]
[TR]
[TD]Mackinnon[/TD]
[TD]335[/TD]
[TD]170[/TD]
[TD]286[/TD]
[TD]456[/TD]
[TD]302[/TD]
[TD]264[/TD]
[TD]156[/TD]
[TD]Byng
All Star: 2[/TD]
[TD]Hart: 2, 3, 6
Selke: 22, 26
Byng: 11, 66
All Star: 3, 3, 6[/TD]
[/TR]
[/TABLE]
6 Years
[TABLE=collapse]
[TR]
[TD][/TD]
[TD]GP[/TD]
[TD]G[/TD]
[TD]A[/TD]
[TD]Pts[/TD]
[TD]Even Strength Points[/TD]
[TD]Hits[/TD]
[TD]Blocked Shots[/TD]
[TD]Awards Won[/TD]
[TD]Awards Nominated[/TD]
[/TR]
[TR]
[TD]Matthews[/TD]
[TD]399[/TD]
[TD]259[/TD]
[TD]214[/TD]
[TD]473[/TD]
[TD]345[/TD]
[TD]286[/TD]
[TD]382[/TD]
[TD]All Star: 1
All Star: 2
Hart
Pearson
Richard
Richard[/TD]
[TD]Hart: 2, 10
Byng: 2, 3, 8, 10
Selke: 10, 16, 27
All Star: 4[/TD]
[/TR]
[TR]
[TD]Mackinnon[/TD]
[TD]409[/TD]
[TD]209[/TD]
[TD]344[/TD]
[TD]553[/TD]
[TD]366[/TD]
[TD]302[/TD]
[TD]178[/TD]
[TD]Byng
All Star: 2, 2[/TD]
[TD]Hart: 2, 2, 3, 6
Selke: 22, 26
Byng: 11, 33, 66
All Star: 3, 3, 6[/TD]
[/TR]
[/TABLE]
7 Years
[TABLE=collapse]
[TR]
[TD][/TD]
[TD]GP[/TD]
[TD]G[/TD]
[TD]A[/TD]
[TD]Pts[/TD]
[TD]Even Strength Points[/TD]
[TD]Hits[/TD]
[TD]Blocked Shots[/TD]
[TD]Awards Won[/TD]
[TD]Awards Nominated[/TD]
[/TR]
[TR]
[TD]Matthews[/TD]
[TD]481[/TD]
[TD]299[/TD]
[TD]243[/TD]
[TD]542[/TD]
[TD]393[/TD]
[TD]307[/TD]
[TD]443[/TD]
[TD]All Star: 1
All Star: 2
Hart
Pearson
Richard
Richard
Calder
All Rookie[/TD]
[TD]Hart: 2, 2, 10, 11
Byng: 2, 3, 6, 8, 8, 10, 33
Selke: 10, 16, 27, 38
All Star: 4, 6[/TD]
[/TR]
[TR]
[TD]Mackinnon[/TD]
[TD]491[/TD]
[TD]225[/TD]
[TD]381[/TD]
[TD]606[/TD]
[TD]403[/TD]
[TD]358[/TD]
[TD]208[/TD]
[TD]Byng
All Star: 2, 2[/TD]
[TD]Hart: 2, 3, 6
Selke: 22, 26
Byng: 11, 66
All Star: 3, 3, 6[/TD]
[/TR]
[/TABLE]
That's an impressive resume by Mackinnon, for the part of his career he didn't suck.
The 3 seasons he played before Matthews was drafted, Mack scored all of:
59 goals
94 assists
153 points
That's an average of 20 goals and 51 points per year.
That's the reason why you shouldn't include a player's rookie and subsequent seasons in comparing them to established players over the course of the same seasons.