You are giving up the 2nd round pick to get Lofton/Mayo. Just like you would be giving up the 4th to get Vilma. In scenario A, you still have a *4th* round pick, but use the 2nd. In scenario B, you still have a *2nd* round pick, but use the 4th.
I understand what you're saying but the move we make at MLB I would like to be as close to a sure thing as possible and Lofton/Mayo, IMO, is lss of a ? than Vilma.
Of course my arguement only makes sense if we were to pass on Lofton/Mayo because we would have Vilma.