It might be possible that you're out of resources, for now, to level up your weapon. But, it's always an excellent choice to fully upgrade the weapon and use it. If you're using Deathmatch on your main DPS, you can freely upgrade it to level 90 and bring out the maximum damage potential of your character. Weapons are crucial when dealing with enemies, and weapons like Deathmatch, which gives crit rate stat, are rare. Feel free to level up this weapon and put it on your primary damage dealer if you don't have a better 5-star option.