Fangraphs Defensive Rating is generous because it is a heavily flawed metric.
Oscar's route efficiency in the OF is worse than Franmil's has ever been, bottom 10th percentile amongst all qualified defenders.
Not only does he take poor routes, he gets poor jumps on the ball. 18th percentile in jump efficiency amongst all qualified defenders.
Couple those together and he makes less outs in RF than the average player should. His -4 outs above average figure right now would be Franmil's worst season since 2018.
Now please, someone go grave dig on how I said Oscar is Franmil-esque in the OF again like I was wrong.