I’ve never played a game when getting exotics is depressing 99% of the time. I wish you would take weapons out of the exotic pool once we’ve acquired them. I know that is something that would benefit the players greatly so it can’t be done. Just wanted you to know though.
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All exotics that you don't have up until Shadowkeep can be required from the fated engrams from Xur every week. Make sure you are on the character on which you are missing a certain exotic. Hope this helps for you to get the exotic you want. Another option is farming 980 nightfalls if you can. This seems to be dropping a lot of exotics.