I'm not going to get into a long discussion about this but last year 21 draftees were out of college. It was 14 in 2007 and 16 in 2006 and 19 in 2005. More and more teams are getting away from the high school kids in the first round and the talent pool most teams are going to are college. So I think it's fair to say the Tazawa was probably playing on a fairly even talent level as most 1st rounders, though not all.
Also, I seriously doubt he will be the #2 pitching prospect in the Sox system. As much as Masterson and Buchholz and Bowden are expected at the major league level this year I think they all still qualify as being prospects at this time. Also Bard, Hagadone and Weiland are all very highly thopught of at present in the Sox system. Tazawa will probably need to show something against AA competition before he's that highly thought of above those six guys.
Lastly, considering the amount of players drafted every year and the amount that actually make it to the majors who project at the draft to be major league talent, I would say that scouts do a fairly good job in determining a players upside level. I was talking all players not just the best or the best.