I know you don't understand baseball, so maybe you've never picked up on this . . . the object of a baseball game is to win. If, all else being equal, pitcher A had a better W/L record than pitcher B, then one can assume he contributed to his team winning more games than player B.
Context is important.
Here's a counter-example: Hitter A goes 1-3 with a double, a fly out and a strikeout. Hitter B goes 1-3 with a double, a fly out and a strikeout. Who had the better game? You'd say . . . "Duh. They had exactly the same game".
What if I added the following context:
Hitter A's double came with the bases empty and two outs in the fourth inning (the next guy pops out), and his strikeout came with two outs and the bases loaded in the bottom of the ninth to end the game.
Hitter B's strikeout came leading off the fourth inning, and his double came with the bases loaded in the bottom of the 8th of a tied game.
Now, who had the better game?