I think the Mythic weapons that are found in the campaign should be like the versions that are in Warzone. I was really disappointed to pick up Nornfang in the campaign and not have it do anything all that different. If it would “ruin the balance”, then make a new skull, or have an option to play with the WZ version after completing the campaign on Legendary.
I was disappointed as well. I picked up Nornfang, “Sweet, this is that sniper that is supposed to be super awesome!”. Turns out it is just a sniper that you can’t pick up ammo for.