He threw 217 innings with a 1.70 ERA. I can't fault anyone for ignoring wins at that point. It would be one thing if he had a low ERA but lacked wins because he was coming out early. That's not the case. He was 11 outs behind Scherzer for the IP lead (and Scherzer had one more start).
This is not a complicated thing: you don't need sabermetrics here, you don't need really anything other than 217 innings, 1.70 ERA. The basic argument for why deGrom wouldn't win boils down to "Amed Rosario can't hit," repeated for almost everyone on that team.