When looking at exercises to improve pitching velocity it helps to think of these exercises as a pyramid where, at the bottom of the period, the exercises look nothing like the throwing and, as you go up the pyramid, the exercises become more and more similar to the throwing motion until you get to the pitching motion itself.
Throwing exercises that are not pitching but closely resemble pitching. E.g., long toss, weighted balls, various other throwing drills, etc.
Exercises that train the muscles involved in throwing in a similar way to how they are trained during throwing but might use different loads and are NOT the throwing (pitching) motion itself. E.g., medicine ball throws. (You could also argue weighted balls go here.)
Exercises the work the same muscle groups as the throwing motion but in a different way than they are worked during the throwing motion. E.g., squats, split squats, lunges, deadlifts, good mornings, shoulder external rotations, push-ups, pull-ups/rows, etc.
Exercises that increase strength, power, endurance but don't necessarily use the same muscles and/or systems that pitching uses. E.g., jogging.
Now, in general, the closer an exercise is to the top of the pyramid, the biggest carry-over that exercise is going to have to pitching. However, if you've spent a long time focusing on one part of the pyramid, it makes sense to bring up other parts.
If, for example, you've never done any consistent weightlifting, it might make sense to use exercises from level 2 and 3 of the pyramid as this is a component of the pyramid that has been neglected. Your throwing sessions will benefit from both the general and specific increase in maximal strength and/or power.