How hard were Ravin and Villarreal throwing when you saw them? In 2010, Villarreal pitched at 92-94. Ravin was not as consistent on the gun...88-94, but mostly 90-91.
I talked to a key Reds exec this season who will go nameless but is near the top of the food chain and asked point blank: Who has the best slider in the org? The answer that came back without hesitation: Pedro Villarreal. I said, "how can you put him above Donnie Joseph, who clearly gets more movement on his slider?" He said Joseph's slider moves so much that guys won't swing at it and it breaks outside the zone. I thought that was interesting. Joseph's slider is not as good because it moves too much.
Off topic, I will say this: The slider that Donnie Joseph threw in 2010 was devastating. Lefthanded hitters often had no chance. Righthanded hitters were swinging at pitches that were hitting them in the feet. That did not work in Double-A, but I am not ready to give up on him yet. He just needs to command the pitch better.