Weighted balls aside, I recently sat in on a pitching / hitting seminar where the coach recommended med ball throws as a method to generate immediate velocity gains.
Looked like this, minus the funny ramp thing...
https://www.youtube.com/watch?v=LA1-uhWlfU8
Not that you are strengthening the arm but forcing the body to engage the legs and core more to pitch (or to swing the bat, same torquing motion really).
I would love to put my son on the gun, have him throw a few pitches. Then do a set of med ball throws, and radar a few more pitches after that.
https://www.topvelocity.net/st...o-pitching-velocity/