OPS and OPS+ are considered to be pretty good markers for a hitter's overall performance.
Looking at game logs, without citing specifics, on the other hand, is just flaky. For example, I choose August 8, less than 3 weeks ago, when JDM went 4 for 5, including 2 doubles and 2 rbi's, in a 9-8 loss to the Jays. Or how about 4 for 4 against the best AL pitching staff, the Rays, on August 11?
The monthly OPS's on the other hand, do show a fall off from April, but the fall off suggests he is roughly an .800 OPS hitter. Am I worried about JDM? Yes. When Shwarber gets walked 4 times in front of JDM, I get nervous.
On the other hand, Cora makes the tough decisions with tons more insight than you or I have, and for now he's sticking with JDM--in a tough race for the playoffs with just 30 days to go.
You absolutely are entitled to your opinion and every opportunity to express it, but that don't make you right. Right now, I think you are, if not out to lunch, at least outnumbered. I got moonslav and Cora. Who you got?