“Rotation is rotation” is one of those baseball phrases that is true enough to make sense, but not complete enough to explain what is actually happening.
You see it a lot with two-way players.
A guy can swing it, produce high exit velo numbers, and rotate with a lot of force in the cage, so the assumption becomes that he should be able to get on the mound and throw hard too.
Sometimes that is true.
Other times, the same guy can hit balls 105 and then get on the mound and throw 82.
That does not mean rotation does not matter. It means rotation is only one piece of the transfer problem.
Hitting and pitching both require the athlete to rotate, but they are not asking the body to express rotation the same way.
In hitting, the athlete is transferring energy into a bat with two hands on the implement, a more stable base of support, and a collision happening out front. Exit velocity can be influenced by bat speed, strength, mass, barrel accuracy, contact point, and the ability to turn behind the baseball.
On the mound, the athlete has to transfer energy into a 5-ounce ball through one arm while moving down a slope, accepting force into the front leg, timing pelvis and trunk rotation, creating layback, and converting all of that into hand speed at release.
That is a much different task.
A hitter can have enough rotational power to create loud contact and still struggle to organize that same power into a throw if the arm action, trunk timing, front-leg block, scapular movement, layback, or distal sequencing are not there.
This is why “rotation is rotation” is not wrong, but it is incomplete.
The better question is not whether the athlete can rotate.
The better question is whether they can rotate in a way that transfers to the specific skill.
High exit velo tells us something about the engine.
It does not automatically tell us how well that engine connects to the arm on the mound.