https://www.polygon.com/2018/6/21/17489932/destiny-2-weapon-customized-slots-loadout

There have been a lot of questions about Destiny 2’s new loadout system coming alongside Forsaken, the game’s next expansion. While we know that shotguns, sniper rifles, and fusion rifles are coming off of the heavy slot, we weren’t exactly sure how the new weapons would slot into primary or secondary categories. Thanks to an interview that Bungie did with Twinfinite, we have a better idea of how things will work.

It appears that weapons will now drop for a specific slot — either slot one or slot two. In the interview with Bungie, project lead Scott Taylor seemed to suggest that the slot assignment will be at least partially random.