Hitters are obviously not picking up the ball well out of his hand, and that is a huge "non-Fangraphable" factor for many pitchers, relievers especially. It's one of the reasons this is a guessing game for the pro's, much less us.
From the CF camera there is no way to know what the ball looks like from the batter's box; you have only hitters' reactions to go off, and those are off-the-scale in Curtis' favor. Even in his ML cup of coffee his problem was more walks (and nerves, and being behind in the count) than people catching a Steve Cishek center-cut pitch and launching it. He gave up 13 H and 2 HR in 13.0 IP despite pitching behind all the time.
If he hides the ball as well as it seems he might, then certainly LH-on-LH you've got something interesting. With 13 relievers you've got room for a 1-, 2-batter LHP.
Personally see this draw at the deck as --- > not the greatest odds, not a Haniger-style or Vieira-style draw :- ) but it is a draw well worth taking. At least it's off the beaten path.