If you believe in Schwarber's 2nd half. Castellanos has been a consistently good bat for multiple seasons, his numbers have been depressed by playing in an awful hitter's park, and he's still in his prime and generally speaking much more of a contact hitter than even good Schwarber. Defensively? Pick your poison. I don't honestly see much difference. Ultimately, what might drive the decision is that all Castellanos costs is money and Schwarber probably has decent trade value after his strong finish. If indeed you could get Merrifield for +/- Schwarber (which may or may not be true), you're not swapping Schwarber for Castellanos - you're swapping Schwarber and $$$ for Castellanos and Merrifield. And on paper at least, you couldn't draw up a guy more ideally suited to address our weaknesses on both sides of the ball than Merrifield.