Example:
7PD
MW Long bow + MW Tatars = (34+6) * (1 + (14*7) / 100) = 79'2 cut damage
MW Long bow + MW Bodkin = (34+2) * (1 + (14*7) / 100) = 71'2 pierce damage
Sometimes, tatars arrows are more useful than bodkin. I am not adding WPF bonus to damage because I don't know how it work, and if someone know, please post. Bodkin arrows is not ever the best option.