Anna Kournikova was never a very successful tennis player but her earnings never reflected that.
Ferrari have a good F1 team, sure, but not necessarily the best; pre-Schumacher, their win rate was dwarfed by both Williams and McLaren. Yet their brand is strong enough that they uniquely can sell old cars to enthusiasts and run them at a profit, were able to get higher payments from the governing body and can license a new circuit (Yas Marina) to include a Ferrari-themed amusement park. All of which gives them a substantially higher baseline income from which to develop their cars.
Professional sports is as much about building and exploiting a brand as anything else in life.
Depending on how you define success, Kournikova was successful. You can't qualify routinely for grand slam tournaments unless you're a top tennis player - you get there purely on merit.
F1 is a different matter entirely. For all the love I have for it, it's hardly a pure sport. But even then, the top drivers do win the top drives. I remember telling my Spanish friend that Alonso was going to win the championship some day, after seeing him routinely out-qualify and out-race his teammate, and drivers in better cars.
Moneyball deals with inefficiencies in antiquated markets, and fits well into Lewis's oeuvre (see Big Short, Liar's Poker for examples of how to take advantage of credit default swaps or the bond market). It has much less to do with "merit," as one can observe a player's true merit over a sufficient sample in baseball. If the guy's a bum, he'll live in Single A for the rest of his career.
tl;dr: baseball statistics are much better at quantifying a player's skills. See "WAR" and the recent Red Sox and Yankees teams for examples.