Now, one could argue that if he'd spent the offseason prepping to play CF and had played CF so far this season, he could be doing a little better than Choo has. But that's not the same thing as saying, if you flipped them today, he'll be better tomorrow.
I do believe Heisey and Robinson as a pair would be better, but Heisey's not here and Robinson's bat won't play every day all summer long, so we either live with Choo's defense in center or we bounce him back and forth depending on who else is playing that day. That's not optimal either. And then, if Ludwick does return for the stretch run and we make the playoffs, Choo's going to be playing center in the postseason. So there's an argument for leaving him there and giving him every scrap of experience he can get.
Having said all that, it certainly wouldn't shock me if the Reds made a July deal for a rent-a-center-fielder.