Gayle has a fast bat swing. He waits with the bat just below horizontal but the bat almost reaches vertical before starting the down swing. He also cocks his wrists very well. He's an incredibly strong man but one if the things people don't comment on enough is how strong his base is and how still he keeps his head.
Sadly I don't think (m)any of us are capable of copying his technique!
This is a very good point and not repeated enough.
Pros are physically very strong! Big hitters manage to generate a LOT of bat speed, high back lift or not. They have a powerful bat swing like golfers have golf swings. We talk about "watching the ball", "still head", and "strong base" but we don't talk about having a solid, powerful bat swing. That in itself is a skill that needs to be practiced separately.