Big debate on the necessity of AAA for hitting prospects. AA pitchers generally have better stuff/velo, AAA generally have better polish but less stuff. AAA is more a holding area for MLB depth, AA has the prospects. Difference between AA and AAA is minimal if actually anything. To answer your question - no one in AAA is blocking the big prospects in AA, but it is not clear the Twins want those prospects in AAA, or if their lack of AAA experience is preventing them from getting the call to the majors at the moment.