Dozier played 289 MiLB games at short and only 47 games at second. MiLB positions are often based on the Peter Principle. Generally, the earlier a guy drops out of a premier position, the less competent he is at that position. Dozier had a chance to stick at short so he was given every opportunity to do so, playing the overwhelming majority of his MiLB games at the position. Despite those chances, he failed at the MLB level. You can repeat those statements for Trevor Plouffe as well. Polanco, on the other hand, has close to a 50/50 split between SS/2B in the minors. Like Dozier and Plouffe, his scouting reports are not optimistic (and, generally, I'd say they're less optimistic than they were for Dozier). Polanco's initial taste of shortstop at the MLB level was... not good. I'm not sure what you're seeing there that indicates Polanco will be an adequate MLB SS. Is it possible? Sure. Lots of things are possible. Is it likely? No. He has a lot going against him. Hell, there are scouts out there who question Gordon's ability to stick at short and he was considered a polished, advanced fielder out of high school. Playing shortstop at the MLB level is really, really hard.