No question that good players are required. Casey Stengel had some great quotes about managing. Earl Weaver did too.
Looking at it a different way, some managers can really f*** things up, whether it's Valentine with the clubhouse and the media, or Ron Washington with the in-game decisions. So maybe the test of a good manager is that they f*** things up as little as possible. Farrell seems to have minimized the f***ups so far.