Winning the game is the goal... However I don't believe that is the point of the conflict.
Lets say there is two games I played one I won, the other well... of course I lost.
The first one I played as my main top laner I had an average of 75-80 cs per 10, 49k damage dealt (to Champions), 28 wards placed, two enemy red buffs stolen, a blue, 4 towers, a inhib... and 7 kills, 2 deaths, and 12 assists... but we lost. I would only get a minimal amount of mastery even if I had the most towers taken in the game, damage dealt and most wards placed.
The second game I could have a quarter of that and have 1/3/8 in kda and still get a massive boost. for a mastery system... It is not that much of a mastery system. From my view point it only represents how many times you have played the champion... not if you have "mastered" the champion.