If you're not going to move them to the standard strikes, at least increase the drop rates to make grinding a little less tedious, especially now that the year 2 NF weapons are randomly rolled.
Or bring skeleton keys back.
For reference, I've run 50+ Sav Song Nightfalls this weekend. Duty Bound didn't drop once and only 6 of my 40ish various teammates had it drop for them.
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The drop of the nightfall loot is increased with higher scores. So the more points you get the better your odds of getting it are going to be. I hipe this helps.