Williams sisters config: big headsize compared high tension

Hello guys!

I do not understand the reason about Williams sisters configuration. Blade 104 around 66 lbs (30kg) A big headsize racquet delivers much higher power and worser control. High tension gives lower power and better control. What can give this config, which better than a smaller, 98-100 sqin headsize racquet on 55-58 lbs?

Thanks.