OK, your are not talking about the claw damage, which is specifically what the trait refers to. I get it now, but back to @JEB's point (I think), they would have to have access to a Large size greatsword to get the 4d6. That is not something that they can randomly or even intentionally get without help from the DM. So there are some breaks on it if it is an issue.
''Hey blacksmith, make a greatsword sized for me.''