Ventura uses his lower half/loads better than nearly anyone.
To me, your biggest bang for the buck would be improving your arm action. It seems a bit long and seems a bit inefficient. Your lower half is pretty solid. Watch your infield throws and your arm action compared to most infielders.
If you were my pitcher, to improve the quickest, I would have you work on overweighted plyoball drills (pivot pickoffs specifically) and weighted ball drills to tighten up your arm action and make it more efficient/quicker. What weighted ball program are you on?