This is bogus. ALL defenses are concerned with yardage first and foremost. NO defense relies that dramatically on turnovers. Any team that puts turnovers ahead of preventing first downs will get burned.
The 3-4 can be an agressive defense, but so can a 4-3. It's all in the style you play, not the base defense itself. Teams can attack from the 4-3 just like they can with the 3-4, and teams can play containment in a 3-4 just like in a 4-3.
An attacking style IS NOT about getting turnovers more than preventing teams from gaining yardage, it's about preventing teams from gaining yardage WHILE hopefully increasing the chance of turnovers.