I don't think the record since that happened really has anything to do with the starting rotation. Because if you look close into those games you'll see Sanchez -- who has been our best pitcher pitched way less than he did before and his starts were taken away by Dickey and Liriano, both doing meh in that role. Happ had a slight regression which was expected, and Stroman was the positive in the rotation. As for Estrada it came out that he wasn't healthy and is pitching with a herniated disk, which makes sense why he's a CY Young pitcher for 4-5 innings before blowing up in the last inning before he gets pulled. It seems like there's a limit where his back goes which makes the fastball and curveball hard to spot and the changup flatter than a BP fastball.
I think he's rusty. Lots of great movement still on his pitches and velo didn't drop, but it would make sense that pitching every like 9 days you lose your touch. His biggest issue has been his walks but his stuff is still there. Also I believe (could be talking out of my ass here but based on what I've seen) he gets better as the game has went on for his past 3 starts. It's his first few innings that are loaded with walks.