World Series winners is kind of a misleading category, though. When you expand it to "Postseason winning teams" including the winners of each LDS and LCS, it becomes much murkier in regards to "ace" pitching. I don't think you can only hold up WS wins as the qualifier for postseason success. In a league with 30 teams where each team plays 162 games, just making it into the postseason is pretty successful. And since there are not that many aces in baseball, when you step back and look at the league in it's entirety, it definitely seems less important to me. An ace obviously can't hold up a team with no bullpen or no power or no speed. You can have a Pedro or a Randy Johnson on the mound every day, but if he is backed up by eight Alex Coras, you're still going to end up losing 100 games. Balance is what is important, in sports, in life, in diet, and especially when having sex in a tree. (FYI, I recommend only doing this in trees with trampolines underneath them.)
As long as a team's rotation consists of at least 3 or 4 guys who could qualify as #1-#3 starters, they should have a healthy chance at winning the World Series every year. Unless it's the Cubs, because hahaha the Cubs.