Short and sweet (a rarity for me), my vote is for Leon both ways because this year for the first time I can see the difference Leon makes with the rotation, which is huge.
JBJ could be the greatest defensive CF is MLB history, which he certainly is not, and Leon would still be more valuable on defense because pitching is the dominant factor in any team's defense and gets tested roughly 120 times per game. And good catchers, as we have seen with Leon, make a difference on how effective those 120 pitches are (even though the lion's share of the work is by the pitchers). Centerfielders get tested--non-routine plays--maybe 2 or 3 times a game, if that.
For JBJ to be worth more than Sandy, I think his OPS would have to be at least .800.
The only complication to my thesis is that on this team Vazquez is still the #1 catcher because of his better hitting, and in my opinion JBJ is still the #1 centerfielder, despite his weak hitting.