As much as I hate the stat...
Dunn: .184/.340/.605 -- .945 OPS
Encarnacion: .300/.404/.625 -- 1.029
Sample size problems abound here. But the real point is that If Dunn got the same pitches to hit that Encarnacion did, you'd see a higher BA w/ RISP. He doesn't get anything to hit, because when does hit it, he kills the ball. When he tries to be more aggressive (as Marty suggested last night), he simply swings at pitches that he can't hit well, and strikes out or hits a ball poorly and gets out instead of walking.
The REAL point should be that both are proving to be great offensive players. You don't have to choose just one. We've got both and should enjoy it.