ERA+ at the time of this post is 131, second best on the team to JZ.
3.02 ERA over 104.1 innings. 3.26 ERA, 91 IP, 16 starts, 2.5 K/BB as a starter. similar numbers as a starter last year over 10 starts. Not enough innings to qualify for ERA title this year until he pitches again, but he's 14th in ERA among starters with 70+ IP (to capture 71 starters, or 4.5 starters per NL team). 3.48 FIP, 4.02 xFIP as a starter. WHiP of 1.21, 1.24 as a starter.
Third hardest thrower among starting LHP in the NL.
I started to do something more exhaustive, but I think it is tough to say he has performed worse than the #3 starters on the Reds, the Braves, and the Pirates (even with Wandy). I'll not even bother with the Giants and just concede the point, but the other above .500 teams (LAD, AZ, St L) have not gotten much better performance.
So, while every 3d start may cause you to shake your head, and he had a rough stretch when he was pulled from the rotation, but, all things considered, Ross looks like a mid-rotation starter on a playoff contender who, for us, is maybe going to get a game a series in the playoffs.