The balance in PvE and PvP is fine as it stands. You have already ruined auto rifles and fusions.
All Bungie needs to do is reduce the special ammo spawns in PvP and also to set them to approximately 1.5x to 2.0x the spawn rate of heavy ammo and reduce the amount given unless using a weapon with associated perks for more (forcing players to forgo more deadly OSK perks).
Special and Heavy ammo should be treated similarly in PvP due to the comparative TTK numbers.
/end rant
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In the time since I posted this, I have already seen a dozen nerf posts for Felwinters Lie. Seriously people.