Hardly the same thing. Cobb was at the beginning of his career, while Hank was finishing up. (In 1907, Cobb was 22. Greenberg went to Pittsburgh when he was 36.) Of course Greenberg's legacy was the same -- he stayed in Pgh. only a year before retiring.
And Robinson was in mid career when he went from Cincinnati to Baltimore. He won MVPs in both leagues. Now there's a Legacy!
The question asks if a Hall of Fame caliber player would have achieved that mark had he played for another team. So here's one ... In 1959, the Kansas City A's and the Pirates were about to swap players. Dick Groat for Roger Maris. Straight up. The Pirates vetoed the deal at the last minute. (See
http://news.google.com/newspapers?ni...pg=4282,980757) Now neither of these guys is in the Hall, but their careers took similar turns -- the following year, both won MVP trophies. Would Maris' career have flourished in Pittsburgh, with its distant fences, as it did in New York (where he was traded later in the same month)? And for most of his New York career, Maris played right field. But in Pittsburgh, Roberto Clemente held that job.
And speaking if what ifs ... Frank Robinson was traded from the Orioles to the Dodgers in 1971 for a boatload of players, including a young pitcher, Doyle Alexander. Alexander became a journeyman, playing for a total of eight teams. He ended his career in Detroit, having been traded there in 1987 by the Braves for another young pitcher -- John Smoltz.