A hammer is a hammer by virtue of it's function, which is a thing designed to drive nails into wood. Anything in the universe, or conceivable, which can perform this function better than anything else, would therefore be the best possible hammer, objectively.
What makes a hammer a hammer? A hammer is a hammer because it does what hammers do. The function of the hammer is what defines "hammer". Anything which can perform that function IS a hammer. However, some things are better at hammering. Those things are better hammers.
You sure like to hammer home your hammer points.Like for instance, I walk up to you wielding some odd tool and say, "this is a hammer." Well, there are many things which can be called hammers, so how well does it perform hammering by comparison? If it performs better, then it IS better than those other hammers. And if it performs worse, then it IS worse than those other hammers.