An interesting question concerning that...
Aren't all these metrics there to help you keep from paying 3 win value for someone who hasn't been one in years?
Whatever the reason, Gray hasn't performed at that level in quite some time. Sure he's a buy-low candidate who may bounce back a bit. Thing is, we've already got Gausman, Newcomb, Julio, Touki, Soroka, Gohara, Fried, and Wright who have just as much chance of being that 3 win Pitcher as Gray does.
Unless trading for Gray somehow gets you Frazier WITHOUT overpaying for either, I'll pass personally. As many have said several times, there's not much reason to go out and get what you already have - if Gray was a legit TOR option things might be different, but he's not. Given his health history, I see very little reason to gamble that he'll get through 2019 more healthy or perform better than Soroka or several others.