[O.B.Left]

Hitting is often described as a straightening right arm pushing the left arm down and out in the downswing.
Wouldn´t the right arm hitting be more solid if the left arm was tightly linked to the chest during the right arm thrust?

If your left arm is tight to the chest then the Hands can not accelerate any faster than that amount which the rotating pivot will provide. If however the left arm separates from the chest , accelerates away from the pivot .....then more hand speed is possible. Be it from CF Throwout or Right Arm Drive OUt.