I think the kid is a potentially brilliant hitter.
What did the Twins' best left-handed hitters of all time---Oliva, Carew, and Mauer---do against lefties in their first years? Julien might never get the that elite level (one too many letters in his name, for one thing), but he clearly has extraordinary talent.
In his rookie year (1964), Oliva had a .270 BA and .677 OPS vs. LHP and a .341 BA and .996 OPS against RHP. Career stats: .271 BA and .690 OPS vs. LHP and .319 and .890 vs. RHP.
Oliva's splits were remarkably similar first-year vs. career.
For Carew in 1967, BA/OPS of .326/.819 vs. LHP and .281/.726 vs. RHP! Career: .310/772 vs. LHP and .336/.845 vs. RHP.
Carew actually started out better against lefties and learned to hit righties over time.
For Mauer in 2005 (his first full year after injury-abbreviated rookie year): .225 BA and .515 OPS vs. LHP in 2005. .323 BA and .890 OPS vs. RHP. Career: .290/.740 vs. LHP and .314/.868 vs, RHP.
Only Mauer shows the pattern that we would hope that Julien follows.
Lessons? The three best left-handed bats in Twins' history show all three patterns: Improving against LHP, staying the same, and actually getting worse.
I'm hoping that Julien follows Mauer's pattern!