Baseball is a two sided game of skill and follow the leader ... do what everyone else does. If you fail to win, it's not your fault. A team assembles some players who hit home runs and wins. Next thing, everybody tries to do the same thing. When they lose, it was not their fault that the other team hits more of them and by the way did not strike out every other time up either. Or the guys with pop all play the OF and every little dink into the gap turns into a double because they can't play defense. (1961 Washington Senators come to mind. Power up the wazoo in the OF. Couldn't catch a cold out there, which is why they finished last.)
As a manager, I could make the playoffs with just about any team you care to name (even Houston, Seattle but those two would need to get some different players) simply by changing how they pitched, put someone in CF who can actually catch the ball and cut the K's on offense down by 50%.
Last year the D-Backs were 29 games better in the win column than the year before. If a team was 81-81 in their last season, it doesn't take a rocket scientist to figure out that if you can win just 10 more games you can be in the playoff hunt and you win 15 more you get to play in the post season more often than not. Every manager loses at least 10 games for simply being stupid about his pitching.
Relief pitchers pitch too often and not enough innings when they do pitch. Not all starting pitchers can even pitch complete game even on their best days. You have to be amazingly good to get thru todays major league lineups 3 times much less 4 on average. Not because they are all that great of hitters, because they have good video and pitchers are creatures of habit. You see a pitcher three times, it does not take a genius to figure out what he is going to throw you this time up. And it's going to be easier to hit because the pitcher is tired and has used up all his adreniline.
Here's an example: You give me Sonnestine and Howell as my 4 and 5 starters and Moore and Nieman to pick them up in the 6th inning no matter what the score with the express goal of those two relievers finish the game ... I win 7 out of 10 against ANYONE. Somedays will be ugly, but those two will get you to the 6th inning still in the game more often than not. So instead of my 4 and 5 starters winning maybe 8 games they win 15 or so.
I have someone in CF who can run down balls in the gap and catch them and I put the ball in play 5 more times on average per game over the course of the games pitched by my 4 and 5 starters - the team will win more games because we will be doing what the other guys are not doing and have the advantage.
If you play with the DH ... piece of cake to score 2 xtra runs per game on average. Have your guy who gets the most hits, hit in the 2 hole and make sure you have guys who can run the bases hitting 9 and 1. Example: Having Ichiro lead off is just plain dumb. He gets 200 hits a year. So you have a guy with some base running ability and a high OBP hit 9 and your typical lead off type guy hit 1. Now you can play run and hit all day, because people will not be able to pitch around your best hitter to get to your normally walking strikeout with pop. So if one your 9 and 1 hitters can or both can get to 2nd base ... and Ichiro comes up once a game with runner in that situation and gets half his 200 hits in that situation, he drives in 100 runs and your pop guys comes up in a situation where they can maybe do some real damage and give your pitchers a leg up.
The object is to win the game and it only takes one more run than the other guys have to do that. Complete games, homeruns, and flash are irrelevant to the outcome more often than not. Just score two runs more per game and give up one less and you will win enough to make the playoffs. It's not rocket science, but you do have to be able to count, which is a challenge for most baseball players and managers.