2nd and 3rd guess
George Sisler and Tommy Harper
I guess because his prime coincided with dudes in the AL like Ruth, Gehrig, Foxx, et al.
Chuck Klein. He was unbelievable. In the year he led the league in SB and HR, he also hit 15 triples and 50 doubles.
The reason why is probably because he played most of his career with the Phillies, who were really, really terrible. He did play on a pennant winning Cub team in 1935.
In that year, 1932, he also led the league in runs, hits, slugging and total bases.
In that year he won the MVP (he was second in the voting the year before and the year after), the Phillies were two games over .500. Not only was it the only year when he was on the team that the finished over .500, that 1932 season was the only year they finished above .500 from 1918 to 1948. (Yeah, they're pretty doggone bad now, too, I know). Most years Klein played for them, they lost over 90 games.
On that single season outfield assist record, he had 44 in 1930. I'd add that to the "records that will never be broken" list.
Based on your hint, Vlad Guerrero.
is about 1/3 of this guy's best total.
I didn't read the hint well, thinking it was also leading the league in assists (rather than all time great season). Vlad did lead the NL in outfield assists in 2002, but he finished 4th in SB and 5th in HR that year, missing a 40-40 season by one home run.
Vlad finished fourth in the MVP voting that year, but arguably should have finished second, ahead of Pujols and Berkman, but behind Bonds.