I agree that for fantasy baseball you want Garza in the majors from the word go. But in real life it is a good move to start him in the minors if you feel there are 5 other pitchers that will do a decent job right away.
And it is mid-May folks. The organization is gonna promote these veterans as viable guys. If Garza pitches strong from here on out and someone viewed by the organization as at this point being lightly penciled in the rotation (ala Ponson or Silva) struggles a lot then you'll see Garza in the rotation right away.
Terry Ryan is a great GM, especially shown by how he does well with a limited payroll and smart draft picks and shrewd trades.
BA 5,HR 9.5,R 4,RBI 6,SB 2,ERA 12,H+S 8,K 11,W 7.5,WHIP 11,TOT 76 pt 3rd