the QB, or fill the holes Dline needs. That of course is over-simplification of the Dline, but for the Oline, technique and working together, footwork, pass vs run block, knowing the plays, reading the "D" are all more technically difficult than for the Dline, where physical attributes of size and speed are far more important than the cerebral part of the game. IMO, a coach for all 3 positions on the Oline (Center, Guard, Tackle) would be far more important than any other position on the field, offense or defense.