We have a literal explanation of how GB operates using game mechanics :
It's Target's HP + Spear Damage which is why it was credited as being able to kill people like Arc even though she's vastly superior in stats.
Obviously not gonna fall into an easy NLF trap to say that it could do anything to niggas like Jiren cause it's a moot point to begin with given the difference in stats of the people involved and how a hypothetical fight would play out , but the point is the damn thing can punch above Cu's weight to serious serious degree based on the Arc comparison of all people.
Not that i expect the likes of Paxton or the others clowns to know that.