This is inconsistent. If 2 IP, 6 ER is an outlier, 9 IP, 1 ER is an outlier too. He may be capable of "spinning a beauty" like that, but it's very rare that he, or anyone for that matter, does.
Also, you don't need to take away starts to conclude he's a better pitcher (when healthy) than a 4.28 ERA. You can make that case easily using readily available data.
He has a 3.68 xFIP (more viable than FIP in thiss case since his current HR rate is insane and he's unlikely to sustain it) and the team he's on sucks at catching fly balls per their overall and OF UZR. If healthy, Peavy will be fine.