I got my glasses a year ago and just did a checkup. Apparently my current vision (with glasses) sits at 21/20. They did two tests using the rotating lens machine.
I might have better vision (with glasses) than a lot of people who wouldn't get glasses because their vision would be good enough.
I'm in Germany and my glasses are mainly used to correct my astigmatism.
For baseball hitting, that would be a colossal advantage.