Here's a slightly different take on things.
I see two players with "star" ability on the Reds list. Mesoraco and Hamilton.
I see a third player who, given his position, could make the "star" list. Grandal.
To me, those are your top three prospects. I understand that they are at different points of development. But these are guys with very rare abilities, given Hamilton's athleticism and baserunning ability, and given Mes and Grandal's talent and position scarcity.
I see two players who, if I'm correct, project as solid players, perhaps starting players, but not "stars." Those are Cozart and Alonso. I'd probably go with Cozart 4 and Alonso 5 because of position scarcity and all around skills. But I can see Alonso 4 and Cozart 5.
I recognize that Cozart and Alonso are well more advanced and more polished than someone like Hamilton. That counts. But in ranking prospects, I tend to put upside as the first order of business. And I tend to put potential stars at the very top.
On Alonso, I think he is being rewarded in the poll for a good hitting stint in the majors. And certainly he can help the Reds. But there are many good hitting first basemen. He isn't a powerhouse guy, like a Ryan Howard. He isn't even a Sean Casey IMO, Sean having "off the charts" minor league numbers, well above Alonso. Nor do I see Alonso as the new Votto.
So I view this as Mesoraco, Hamilton, Grandal, Cozart and Alonso as the top five, for those reasons. All good prospects, just a different view of the order.
And, by the way, if these are the top five, I have Boxberger at number 6. Again, huge upside as a potential closer. If Box was a starter, with his stuff, he'd be even higher IMO.