I get what you're saying and I normally would agree. But he shouldn't get knocked down playing 2B in his case. That was his best position... Period
So the workaround to make his fielding attributes work within the confines of the game, is to just switch his primary position to 2B. Raise his defensive attributes to make him the better fielder he was there. Then he gets the Secondary position penalty when at 1B.
Trust me. It works and it's a simple fix within the confines of the game. I'm more concerned about his actual true life performance level at a given position than just for labeling purposes at a Position within the game that artificially makes him a weak fielder at 2B. That's historical accuracy even if he did spend most of the 1947 season at 1B. He was a better 2B. Before and after that season.