Given that almost every weapon type actually uses a mixture of blunt, slashing, and piercing, I don't think there was ever an intention of realism — they simply wanted arbitrary, categorical synergies that might slightly adjust gameplay based on composition. I mean, have you seen the blades on those Monk patas? How is that not piercing during a True Strike? How is Riot Blade not? Heck, Chaos Thrust was originally considered 2 hits slashing, 1 hit piercing in 1.x, when the strikes were separately calculated.