Looks to me the problem with Giolito is that he cannot locate his pitches. He's mixing in the breaking balls but can't throw effective strikes with his fastball. Also no one has discussed why a guy who was throwing 97-98 dropped to 94-95. It all sounds like some type of arm problem or at least a tired arm. After the TJ surgery he doesn't want to say he is hurt.
His average FB has not dropped more than 1 MPH, from Janes' article the other day. He hasn't lit up the radar gun with 97+, but hasn't been that big of a drop. Consider also his age, IP beforehand, and that it's August/Sept. He's still learning. You're exactly right though -- he has not been able to spot the FB, which causes him to be more reliant on it in hitter counts. As Elvir said, the curve is not, right now, a pitch consistently a strike (which would be fine if he was setting up hitters with the FB and CH). Early returns have not been good, but the velo is not the issue right now. Don't be "troubled" by something that's not true, just because we aren't seeing cool 99 MPH pitches.