Minor spoilers.
In the “Legends Lost Weapon Quest,” you can be rewarded with the perfect paradox. My Name Is Byf made a video Saint-14, The Perfect Paradox(https://youtu.be/Ciy4WIKbTI4), he speaks about how we will one day experience time travel, his theory was that we will learn it through the Vex or maybe even the light its self. I believe that we will experience it through the Exo Stranger. The Strangers rifle says, “Ghost’s analysis suggests this weapon has been exposed to incredible forces…and that parts of it shouldn’t yet exist.” This hints towards the stanger being the way we will “give” the Perfect Paradox to saint-14 through time travel.
Just a little theory
Why would we gift it to him?
That is a good question.
The gun itself is a paradox hence the name, however, we can’t be sure why we would give it to him. Maybe we knew he was going to the infinite Forest and we gifted this weapon to him, maybe Osiris asks us to give it to him, maybe even the Speaker. Whatever the reason I do believe we will go back in time to gift it to him.
It’s possible it was the Speaker who made it. It has his name in the beginning flavor text. I just read the lore tab, so I can see how you think it would be us as well.
At some point in the future, we will have to at least meet Saint-14, because in the lore tab for Helm of Saint-14, Cayde-6 & Shaxx talk about how Saint-14 says he’s seen us in the future, and that’s why he fought at Six Fronts. In Perfect Paradox’s lore tab, Saint-14 is talking to us and about how he is trying to follow our example, because he’s seen the city and how we make it. How also talks about how he’ll evntually try to get the gun back to us, because he says we were the ones that gave it to him in the first place. I don’t know why we’d give him the gun, but at some point we’ll meet him, and we will.