A pitcher that was good enough to rise through levels of minor league ball after about 12 games a level and makes a major league debut yet does not rise in the rankings would seem rather incongruouswith top of the rotation potential.
While MLB may be underrating one or more of Balazovic, Duran, and Graterol compared to a couple other publications (FanGraphs has all three at a lofty 50 FV), I think it's also important to realize that there are a ton of really good pitching prospects out there at this time.
I'm far from an expert observer, but my sense is that the Twins have a decent but not great comparative advantage when it comes to premium pitching talent, maybe a bit above average. In the AL Central alone, there may be as many as 10 pitching prospects in the other systems who are as good or better than any of these three. CWS and DET probably have superior pipelines nowadays, and KCR isn't that far behind, and all of those clubs will pick before we do in the 2020 draft, which is supposed to be exceptional in terms of both first half of the first round talent and overall depth.