Do you know why we privilege the original? Because it's bloody original, that's why.
You can argue that the technical chops required for producing a good copy of the Tyrannicides or what-have-you are impressive. This is true. But if you're copying something, you have the inestimable advantage of working from the original, and you (obviously) are not inspired as was the original's creator. What you are doing is craft; what he did was art. Now, you may also be an artist. But rote copying is really not art.
Will it look as nice in a museum? If it's a good copy, yes. Is it the same level of art? No, it is not.
There is something that happens in the moment of composition that is only present in the original. Yes, I am invoking the Muses. They seem germane.
If we find out that Harmodius and Aristogeiton are themselves copies, they are still fine statues. But they will lose status, which will then be conferred on the true originals. There is nothing wrong with this. There really isn't. I promise. Some things are actually prior.