The harder difficulty levels do a good job of mimicking the strategy of a real at-bat. The pitch aim indicator appears very late so you don't have time to make square contact unless you anticipate the pitch location. So if you're looking for a pitch on the outside of the plate to drive, and the pitcher pounds you inside with a fastball, the best that you can hope for is to foul the ball off. You can also change your batting stance to alter your plate coverage from pitch to pitch. As a pitcher, you must choose between the pitches in your repertoire and then aim at a location.
Most pitchers have four pitches to select from, although some relievers only have three.
There's also an option to give each pitch an energy boost. This means that for a critical pitch you can rear back and throw that fastball a bit faster, or give that curveball a sharper curve. There are still some bugs in this feature, as I've seen a few 120 mph fastballs. Using the energy boost also tires out your pitcher quickly, so you need to pick your spots. Ramiro Mendoza in his wind-up.