My theory is that defense is cheaper and more reliable than spending all that cash just for your offense to have an off-night. Any great offense can win games but usually the champions are teams that bring the great defense. It goes without saying, and I know it sounds cliche, but offense wins games, but defense wins championships. However, above all else, it's better to field a team that is cohesive offensively and defensively because whenever one has an off-night, the other needs to step up.
My opinion is that it never hurts to field a defensive team. In the world of BB, it's cheaper to build around defense first followed up with complimenting that defense with offensive skills.