there is much more to be athletic than straight line speed and reach. This isn't boxing or the 100 meter dash. This is baseball and athletic timing, hand eye coordination and agility all factor into being a good defender. Eloy, frankly, has none of those things defensively and it's why the metrics grade him worse than Vaughn, as does the eye test.
Notice how Vaughn hasn't even come close to any collisions? That's something you risk every single night with Eloy and LF -- and he could take Robert out with him.
It's not an acceptable risk. Eloy is almost certainly going to be at best a part time fielder.
