Ed Kilgore is very correct here.
"There are a lot of close gubernatorial races out there (Cook Political Report's Jennifer Duffy rates ten of them as toss-ups), so you'd think if there was any genuine GOP "wave" underway we'd see it in these contests. More likely, the perception of a "wave" is mainly the product of a crazily pro-GOP Senate landscape."
Similarly, generic ballot numbers show a small and steady Democratic edge. If the Senate races weren't being fought in so many red states, no one would be talking about a wave.