The problem isn't 'we should've traded someone'. Every team in baseball could make that claim. I think the board was divided on Yoshida's contributions. Maybe 40% of us liked the guy, but understood the balance issue. And everyone else wanted him gone at all costs.
But there was no reasonable way to predict Yoshida's good start and Duran's weak-ish start. Had we traded Duran, and gotten a .550 OPS from Yoshida, we'd have had a problem. And 6 weeks from now, we might be very happy we kept Duran, for a wide variety of reasons.