So a better question is...do you need to draft (or sign as an amateur FA) and develop your hitters to be effective. Of the starting 9 (I'll say projected starting 9 in case of current injuries) of the top 10 offense in the majors this year, I'll figure out the D&D hitters:
Red Sox 6
Mariners 2
Indians 5 (4 depending on what OF you put out for Brantley)
Cubs 2
Cards 4
Jays 1
O's 3
Tigers 2
Angels 2
Giants 4
5 worst
Braves 1
Phillies 5
Reds 5
Royals 4
Yankees 3
From this I conclude that nothing was proven...you can win without drafting and developing or you can lose.