I have noticed that the new Oathkeepers damage buff is not applying to Leviathan's Breath, at least on Kalli. I have tried Wishender and it worked just fine. I also don't know if this is just a Kalli thing or not, so a bit more testing needs to be done. If Bungie said anything about the buff intentionally not working on Leviathan that's my bad and pleas let me knwo but I have not found anything in the last TWAB so yeah.