I was never a pitcher, but I did play a lot of baseball (3rd base) but, funny enough, I've actually been playing disc golf longer; though not seriously.
Anyway, after all these years of playing, I never even tried a thumber until 2 years ago. I always threw tommys and just varied the angle of my wrist on release to get the disc to go one way or the other. The kicker was, I could never get distance...just never thought about it. After seeing some videos of people bombing forehand and seeing my buddy Steve do it in person, I started working on it. I started with line drive thumbers, then moved on to distance. I'm still no 300 foot overhand crusher, but I'm a little more reliable.
To the OP: you'll hear lots of different opinions, but I would certainly listen to the guys who can throw overhand 300 feet or more with control. There's more than a few on these forums, to say nothing of the OH killers in the thread here. Just like any shot, it requires practice. The thing with practice in disc golf is that you have to work with your body. You already have a baseline, since you've been throwing OH already you have a good idea of how your body reacts. Now there's nothing to it but to listen to the advice here, grab discs of different stabilities, and work on it until you nail it.
It also helps if you can take video of you throwing OH. You'll get even more great advice that way.