Hitting is complex, so of course there are many important aspects to it. But what is the most important? Competitiveness? Athleticism? Bat speed? I am going to argue none of the above, although they all matter.
I believe one of the most underrated aspects of hitting is seeing the ball. The ball has all of the information we need. The ball tells us how fast and in what direction it's traveling. It also tells us how fast and in what direction it's spinning. Our mind then uses this information to project the rest of the pitch. The more accurate a projection we make, the more accurate our swings can be. But if we don't pick up the information from the ball, we're taking a shot in the dark.
It's easy to say we saw the ball, but we can always see it better. Challenge yourself to see the ball as well as you can, especially in games when emotions are ramped up.