I was one of those people but in slight defense of Rosario, the kid brings it with the glove. That in itself means he won't go entirely 2015 Danny Santana on the team.
The most concerning thing about Rosario is that he has doubled down on his worst habits thus far in 2016. Somehow, he's swinging even more often than he did last season and actually making contact less often.
But I'm one of those neanderthals who thinks corner OF defense isn't worth worrying about. And in any case, I doubt there's significant difference in defensive ability between the two, so it's mox nix from that angle in terms of Kepler/Rosario.
As for swinging more often, yeah, but I wonder how much of that not so much him actually swinging more, but is the league figuring out there is virtually no limit to what he'll swing at.