Of course it's all about the pitching. But you don't need your "ace" to be the one that pitches that way. For as great as Kershaw has been, he's largely been a playoff dud. Whereas other, lesser, pitchers have thrived. And from year to year things are pretty erratic. 5%? C'mon. 50% of the teams in the last 6 years haven't had an ace. That's just the last 6, your 5% is sort of silly on the face of it. Even if taken as hyperbole. And much of your point is unrealistic about how available and plentiful actual aces are. I believe we missed a chance at one this offseason (and was highly critical of it), but there aren't enough aces to go around. And those that have them rarely let them go. And sometimes when you have one you still get beat. (See: Johan Santana's run here. Or Chris Sale last year. Or, again, pretty much every time Kershaw has pitched) You should always go get great players when you can. But you don't need an "ace" any more than you need "at least 40 homeruns" from your 1B. You need as many good or great players you can get and you need them to show up when the small sample kicks in.