The rotation of the body is easy to do, but many people don’t know that there is a short pause in the rotation. This pause makes you swim way faster.
The energy transfer between arms and legs is what makes you move well in the water. It doesn't matter if you use your legs a lot or a little.
Many call that transfer of energy body rotation. But if you look at it in detail, the whole body doesn’t rotate at the same time or to the same degree. Doing that is a big mistake.