In the other sports you can (somewhat) scheme your way around a talent deficit, especially if it is not a large one. In baseball you can't do that. There is no different way to pitch to guys on the other team that might even things out, there is no odd ball defensive strategy that can overcome better hitting, nothing like that.
Which is why it made me laugh the other day when I happened to be in the car and listening to the FAN to hear if they made any trades, and one of the dimbulbs on there was talking about Shelty and said that he wasn't a manager like a Chuck Tanner was, a manager that you knew would win you 14-16 extra games a year (note, it might not have been exactly 14-16, but it was in the teens). The idea that any manager, the best manager in the world, was going to win you 14 extra games in a season is mind-bogglingly stupid. And the fact that one of those guys suggested it made me remember why I don't listen to local sports talk radio anymore, and haven't for a couple of decades.
Yeah, that's a pretty bad take, which is not abnormal for them. Some of the stuff I've heard Starkey, Cook, and Dunlap say about Pitt over the years (such as there being no excuse for them not being a top 25 team every season) just showed a stunning lack of understanding about how college football works.
But yeah - any baseball manager worth 14-16 wins/season would be sitting on a golden throne in New York City with his own secret service team. That's a higher WAR than the best of the best. Even if a manager makes a crafty or piss poor decision late in the game, that didn't singlehandedly win or lose the thing. You'd have to take into account every other decision they made in that game, also, as well as plenty of the things said manager did before that game even began (obviously it's not a quantifiable statistic, which I suppose lends itself to proclamations such as the one above).