This could be from the land of hot takes, but there are two factors in what makes Duran a crappy outfielder. First, he's lazy, and second, he's a coward.
The ball that went over his head Saturday night, he JOGGED back on it till he realized how well it was hit, but by then it was too late. We were taught to read, go AFASY (as fast as you can) to where you think it'll be, and then get under control. Duran just jogs.
Yesterday, on the two alleged triples (I feel bad for Schreiber getting charged with earned runs there) you could see he was afraid of the wall. He doesn't have enough kinesthetic awareness to sense when he's getting close, and seems afraid to go hard into a wall. The out is not the most important thing to him, his safety is. He's obviously done the research on that.
FWIW, I played centerfield through community college. We were taught to put an arm out to sense the wall if there was time, but otherwise, track the ball. I had some fun accidents with walls and fences, but my favorite was running full speed into a 3' high chain link fence, flipping over it, and losing the ball when I landed. Probably not a home run, but I carried it over the fence with me.
Bottom line, he sucks defensively and he's not going to get much better.