Diaz had 3.5 WAR (going by Fangraphs) in his great season in 2018, and he probably won't top that this year (he's at 2.3 WAR). Five Mets position players and one pitcher (Scherzer, despite the injury) rank higher. I don't think you can make a realistic MVP case for him. As for Cy, I'm not categorically against awarding relievers but they not only have to be exceptional, there can't be a really deserving starting pitcher. And Alcantara is deserving, at least as of now.