Kemp is a top 15 offensive player. His WAA and/or WAR are flawed and incorporates his defense. The vast majority of Kemp's playing time has come from CF, where is the worst. DET would put him in one of the corner spots, preferably RF, and his lack of defense would be no different than J.D. Martinez'.
Again, trade Kinsler's $16 Mil for average 2B production for Kemp's $21 Mil above average corner OF production. You don't see the benefit?
Add to the fact Castellanos was the worst 3B in the MLB, hands down. His improvement on offense will never make him better than an average position player (above average DH maybe). He would have to develop into a top 15 type offensive player, and that IS NOT what he projects to be.
You cannot take on salary like Kemp's without voiding of salary someplace else. We voided Fielder and took on Kinsler, plus $30 Mil to Tex. If we can trade Kinsler to LAD with Castellanos and got Kemp, Guerrero and $30 Mil, what isn't there to like. This trade works for both sides.