I think it's a valid question why Sonnanstine (87 MPH fastball) and Kevin Slowey (90 MPH fastball) are acceptable comps for a guy whose value, in part, comes from plus velocity.
I mean, there are lots of guys who excelled in AA. Why would those guys spring to mind?
You could pick a guy with a good fastball/curve combo like Gavin Floyd who ripped up AA and hasn't become what he was projected to be in the majors, but comparing a plus velo guy to two soft tossing strike throwers doesn't make sense.
Why those guys came to mind was the BB/k ratio, in high minors, at a comparable age. as for the velocity, yes, they are bad comps, as I acknowledged. It's the control that brought them to mind.
Oh, and before any trashes Slowey much, he was BA's minor league pitcher of the year and had a a pretty good second year in the majors (<4 ERA and 1.15 WHIP) before injuries.