The key is the shaft. Each shaft gives you different characteristics so you can optimize your shot. I am a bit steeper with my swing versus flat like a Matt Kuchar. To combat this, I could use a shaft that has a higher flex point (or kick point). Also, the stiffness of the shaft plays a part as well. A shaft that is too stiff might feel like you are swinging a telephone pole while one that is not stiff enough will feel like a buggy whip. The torque of a shaft is how much twisting is allowed. Faster swing speeds require a stiffer torque.
Launch monitors will give you all the stats that can be optimal for YOUR shot. This all depends on swing speed, ball speed, launch angle. The shaft is the engine that controls all these factors.