We've tended to think that the Eagles went defense heavy in the 2012 draft because their first 3 picks were all on that side of the ball. However, 5 of their 9 picks were on the offensive side of the ball. All told, it was a very balanced draft. That wasn't the case for all teams though, as 5 NFL teams used at least 75% of their picks on one side of the ball.
It does make some sense to go unbalanced. If you're a team like Green Bay, who scored a ton of points last year but had a poor defense, you load up on D (6 of their 8 picks). Only, historically this hasn't appeared to be the case, at least one side of the ball.
ESPN looked at every draft class back to 2002 (1st time there were 32 teams) and found 18 instances of a team using 75 percent or more of its draft picks of offense and 15 instances of a team using 75 percent or more of its picks on defense.
12 of those teams who loaded up on offense saw their scoring decrease the next year and their defense actually get worse. 13 of the offense heavy teams gave up more points the following year.
For teams that went defense heavy, there was very little correlation. A near even amount got better on defense as got worse.
The point is here that you shouldn't expect a quick return on an unbalanced draft. Taking all offensive players may have a positive effect on that side of the ball years down the line, but history shows that its not going to pay quick dividends.