JBJ in AAA: .278/.379/.498, .877 OPS, 143 wRC+
Ellsbury in MLB: .305/.366/.440, .806 OPS, 118 wRC+
Not sure how you can conclude that JBJ isn't ready. You're going to have growing pains with every rookie, sure, but that doesn't mean he's not ready. He's an OBP machine that can hit for at least a little power, and he's already a 70 (on 20-80 scale) defensively.