Stats show why only six players should bat: OPS for 7, 8, 9: .698, .694, .579

Pitchers have OPS .336

Sorted by batting order:
3: .830
4: .800
2: .769
5: .769
1: .760
6: .739
7: .698
8: .694
9: .579 (National Conference: .512; American Conference: .645)

Sorted by "position":
1B: .793
3B: .789
DH: .773
2B: .771
RF: .769
CF: .743
LF: .737
SS: .728
C: .706
PH: .649
P: .336

Pinch hitting for the pitcher doesn't help much.

From: http://www.baseball-reference.com/leagues/split.cgi?t=b&lg=MLB&year=2016