Everyone thinks Wang is due for some regression because, typically, pitchers good at generating weak contact are also good at missing bats. Wang doesn't miss bats, and he doesn't generate the weak contact that so many Yankee fans claim he does. His BABIP was right about league average, and BABIP is essentially a gauge of how hard the ball is getting hit. I watched more than 1/2 his starts last year, and he seemed to benefit a whole lot from the ball being hit right at a fielder. When someone was on base, these resulted in a high amount of double-plays (which aren't happening if the ball is hit weakly). His xFIP was 4.35, which is where I would expect him to pitch going forward. A low 4 ERA is good in the ALE, so he'll be a serviceable middle of the rotation pitcher. Good, but not remarkable.
Oh, and, he doesn't have the best sinker in baseball. Brandon Webb does. I also question how much of his success is due to his sinker and how much is due to the Yankee grounds crew. ERA of 3.03 vs. 4.35 and G/F ratios of 3.27 vs. 2.41 at home and away. With the range on display in that IF, I think the grass is allowed to grow a bit. There's nothing wrong with that, but it is a factor to consider when rating Wang's talent.