If you're a free-to-play player or battle pass user, I won't recommend you refine the weapon. 5-star weapons are rare to obtain, and it's better to have copies of them. Suppose you're in a spiral abyss where you need two teams on both sides. If you have support characters on both teams that can use Amos bow, then having two of them will benefit you. Unless you can afford to heavily spend on the game, and risk the chance of getting another rated weapon, avoid refining Amos bow. Personally, even if I get an extra copy of a 4-star weapon, I level up both of them separately. Always prefer to have versatile gameplay, and you'll have better team compositions.