Average? He's the third best hitter at his position. Streaky I will grant you
Let's not exaggerate. He might be better than average, but there is no way he is the 3rd best hitting LFer.
Last year Away for LF (150 PA min, assumed park neutral stats)
35th in RC+
35th in wOBA
Last 2 years Away for LF (300 PA min, assumed park neutral stats)
24th in wRC+
24th in wOBA
Last 3 years Away for LF (450 PA min, assumed park neutral stats)
13th in wRC+
13th in wOBA
Last 4 years Away for LF (600 PA min, assumed park neutral stats)
20th in wRC+
20th in wOBA
Last 5 years Away for LF (750 PA min, assumed park neutral stats)
19th in wRC+
19th in wOBA
His actual Away Stats
2015 = 92 wRC+ .307 wOBA .312 OBP .402 SLG .714 OPS
2014 = 104 wRC+ .322 wOBA .307 OBP .427 SLG .734 OPS
2013 = 140 wRC+ .375 wOBA .372 OBP .488 SLG .860 OPS
2012 = 84 wRC+ .298 wOBA .326 OBP .344 SLG .670 OPS
2011 = 108 wRC+ .332 wOBA .328 OBP .439 SLG .767 OPS
2013 is the outlier here. Without it, his last 3 years Away stats would beg to say below average. With it, he is barely above average.
I do not know any top 5 hitters for their positions who have such a problem hitting on the road.