Yeah, 2014 wasn't really a Republican wave on the Senate level. They won all the Romney states, yes, but they barely managed to win CO against a terrible Democrat and underperformed in several Romney states. That's why this idea that 2018 is going to be a Democratic wave year in the Senate is exaggerated. I think the general trend we're seeing is that blue states are electing Democratic Senators and red states are electing Republican Senators (even though red state Democrats are still much better off than blue state Republicans).
Of course you also have to remember how retirements hurt Democrats badly. Harkin and Johnson may have won reelection if they wanted to, but Rockefeller and Baucus would have likely still gone down (the former supported the war on coal, the latter wrote much of Obamacare himself). And partisan trends finally caught up to Landrieu and Pryor.
