Batting average, it doesn’t determine the “skill” of the batter alone, since doesn’t take into account things like BABIP. Home runs, every park is different, so flyballs in certain parks could be home runs in other parks- not fair.

The concept can be applied to virtually any stat because: (A) a great deal of other stats are attributed to the individual, but are realistically team stats, as mentioned (RBI, ERA, etc.), or are in some other way affected or influenced by outside sources (Ks are dependent very often on the catcher framing the ball, and/or an umpire’s generous strike zone, Home runs are dependent on the particular field someone is hitting them at); (B) Plenty of other stats have seemingly arbitrary values attached to them (Quality Starts, for example; why is it quality if you give up only three runs, over six innings? Why not four runs, over seven?).

RBIs and runs are heavily team-influenced, but they measure things actually produced— which is to say, I do this, then THIS happens. (A player scores a run, and/or makes another player score a run with a batted ball or BB.)

Wins are “awarded.” No pitcher ever produces a win, really.