Coming from it slightly in the reverse direction, there's a lot of .200 ISO guys, which would make for a good study (for someone with better database skills than me) but is time-consuming to spot check by hand. Just looking at the top 10 guys in MLB this year (.280 and above), the guys like Arenado, Duvall, and Bruce had 20 homer seasons in the minors while in their late teens or early twenties. Ortiz, Rizzo and Bryant were all considered power bats as prospects. Story, Machado, they had double digit HR as teens and brought up young enough that their power was still developing. Lamb and Carpenter reached double digit HR while a little older in the minors, so might be examples of what you're describing, but hardly under the radar to the scouts rating them, I'd have to think. Expectation versus ceiling, might be the farthest you could distinguish.