There's a better way to look at this
Look at Ruth's career BA, OBP, SLG, BB%, K% etc compared to league averages during his career.
compare them to the league averages now.
If Ruth's BA was ?30%? (pulled from an orifice) better than the league average for his career and the league average batting average in 2012 was .255 then a 30% better batting average would be .331