User blog comment:Fistful of Force/Tactics: Defense./@comment-76.93.220.23-20121116081116

It all depends on what champions are attacking and defending. Varus/Anivia/Sona can hold off five enemies for quite a while, whereas Ezreal/Ahri/Soraka isn't nearly as effective.

It all comes down to who has better zone control. Even if the sieging team decides to go for the turret, a trio with good zone control (strong AoE like Anivia/Amumu or piercing/AoE range like Varus) can defend very effectively.