The difference in positional adjustment between shortstop and third base is five runs per 162 defensive games — meaning that, were Ramirez a true-talent 5.0 WAR player at short, he’d be a 4.5 WAR player at third.
I know you added the UZR afterward, but this is extremely misleading. The 5-run difference in positional adjustment for 3B/SS is based on the fact that, on average, when a player moves between those two positions, his defense improves/suffers by 5 runs/year.
I haven’t looked for, but wouldn’t be averse to reading, a study on how players perform in their first year after a position switch. It’s certainly true that most third baseman would find playing shortstop more difficult, but a slightly different set of skills are emphasized in playing third, too.
ARod, for example, had a total UZR of ca. +24 for the two years before moving to the Yankees. The next three seasons (at third base) were a combined -6. His numbers are better at SS per Total Zone, as well.
Obviously, there are other variables present in both ARod’s and Ramirez’ situations. All I’m suggesting is that it wouldn’t be surprising if Ramirez’s defensive numbers didn’t immediately rise.