You have a few things wrong here:
1. Your acting like a sentient hammer that moves of its own will doesn’t work with usopps sniping combat style. Due to the hammer being able to move on its own, it can be used as ammunition because it’ll return to Usopp post shot. Usopps sniping isn’t about him shooting a bullet out of a gun, it’s him shooting various abnormal and unique “Stars” at his opponent. And seeing how he’s used a “Hammer Shooting Star” in the past, idk why suddenly a hammer is now not aligned with his combat style.
2. This “god tier weapon” debate sounds like the same stuff people said about Zeus and Nami. Oda using top tier weaponry as a way of making the weak SHs viable in modern day combat is not out of the ordinary. Also I don’t think Ragnir is God Tier. Loki isn’t God Tier with it, despite having multiple other insane powers?
3. Ragnir in no way throws away Usopps core character, it enhances it. Usopps not going to become a head to head fighter with Ragnir, he’ll still be a liar, who can bluff his way to victory. A hammer that can be sniped, and hit an opponent on the return means that Usopp can set traps for his opponents using it. Such as shooting the hammer, having it “miss” to lower his opponents guard, then having the hammer knock them out by hitting his unsuspecting opponent from behind. Sounds like the perfect way to counter a teleporter like Van Augur as well. And none of these ideas are new, the Mjolnir theory’s been one of the oldest Usopp theories out there
4. Usopp Hammer being iconic is in no way cap. You mentioned two of Usopps most iconic scenes, now let’s not act like the pose with the 5/10 Ton Hammer isn’t up there as well. It certainly is because it’s one of the most famous poses for Usopp.
5. Loki is a minor character? He’s the arc royal that Luffy saves and befriends during the arc. And Nami got Zeus in an arc about a weather controlling witch, who Nami has been unknowingly connected to since Thriller Bark due to Lola.
I think you’re just misconstruing usopps fighting style where you don’t think Ragnir fits. But if you look back at it. A legendary hammer from the island connected to usopps dream that can be used as a shooting star and return to his hands or be swung with immense weight despite usopps physical weakness because it chose usopp for his heart and spirit is 100% aligned with his character and the perfect power up for someone who needs a sudden and immense boost like Usopp does going forward