He's still one of the best
Rod Carew, same thing. According to the Hall of Fame, he's a second baseman, but he actually spent more than half of his career at first base. Harmon Killebrew is listed as a first baseman, but spent less than 40 percent of his career at first base. Killebrew is a different case, though; while he spent much of his career in left field or at third base, he did play first base more than anything else. So if you have to assign him a position, that's the one. But of course that reasoning does not apply to Banks and Carew. Based purely on playing time, both should be considered first basemen.