Elemental primaries are bad for the game for 2 reasons. #1 They make kinetic damage primaries irrelevant. This is why you never saw anyone using them in PVE. #2 Elemental primaries make heavy and special weapons less useful. By only allowing kinetic damage primaries Bungie has make these other weapon choices more relevant. Aside from elemental burn in the Nightfall there really is no need reason to have elemental primaries anyway. You take an enemies shields down with a heavy or special weapon, then switch to your primary and finish them off.