I don't think your analogy holds up.
Koufax played 12 years but only six of those were productive.
165 career wins......192nd of all time
2324 Innings..........270th of all time
Compare that to Jim Brown:
9 Seasons..all productive
12,312 yards..........8th best of alltime
5.22 yards/carry......1st place all time
Your comparison might be better with Gale Sayers who many feel may have been one of the greatest had he not tore up his knee...
Year TM G Att Yards Y/A TD Rec Yards Y/R TD
1965 chi 14 166 867 5.2 14 29 507 17.5 6
1966 chi 14 229 1231 5.4 8 34 447 13.1 2
1967 chi 13 186 880 4.7 7 16 126 7.9 1
1968 chi 9 138 856 6.2 2 15 117 7.8 0
1969 chi 14 236 1032 4.4 8 17 116 6.8 0
1970 chi 2 23 52 2.3 0 1 -6 -6.0 0
1971 chi 2 13 38 2.9 0 0 0 0.0 0
TOTAL 68 991 4956 5.0 39 112 1307 11.7 9
http://espn.go.com/classic/biography/s/Brown_Jim.html
Sporting News rated Jim Brown the greatest football player of all time
http://www.sportingnews.com/nfl/100/1.html