At some point he's probably not going to turn a corner in mid-season. The guy is ancient by baseball standards, so even with his relatively low-attrition techniques his ability is eventually going to end. Who knows when it will happen, though? I also hate the insistence on having to wait for a guy to find himself until mid-season, though.
But I don't even really think he's been all that terrible. I mean, I hate watching his starts because I find those games to be low energy (all the wasted pitches, full counts, etc.) and totally frustrating (passed balls, wild pitches, random clusters of walks).
Dunno, if I were in management I might try to line up his rotation spot against more SP4s and 5s. Might help mitigate the perception of him being absolutely terrible.