The knock on Robles isn't that he can't hit, it's that he can't hit for power. Until recently, going back to the days of legal spitballs, a slick glove center fielder with a ton of speed and a cannon for arm was all you wanted. If he could hit .275 and draw some walks, that was all gravy. Now, they're expected to hit 20 homers as well. That's a tall order.
With what the Nats gave up for Eaton, there's almost no chance they don't exercise both option years, assuming he's not injured. He's actually playing well, and his contract is cheap.