The season has gone for about six weeks, but Harper's walk rate -- about 19% -- is Yostian. That is, Eddie Yost often led the AL in walks, with a walk-rate of 20 - 22%. Frequently, Yost had an OBP over .400 and finished with a lifetime OBP of .394...across 18 seasons. Yost and Ted Williams were so good that umpires let them call the close pitches. If Yost didn't swing, it was a ball.
Yost had power that the old ballpark swallowed (until about 1956 it was 400 feet down the 3B line), but nothing like Harper's power.
Harper hits them like Harmon Killebrew did in 1959, at age 23, when Killer walked about 14%. Furthermore, Killebrew hit behind a guy who hit 31 home runs and ahead of a guy who hit 33. Another mid-lineup guy only hit 21 homers, because he was hurt, but had hit 39 the year before and 42 the year before that.
Some guys play as if they are meant for a slightly higher league than the majors. In the NFL, Sonny Jurgensen played as if he was a heart-beart (or two) ahead of everyone else. Harper is still improving, but this season, he looks like he's headed toward that MLB Extra league.