How can we tell the difference ? It seems to me that the only way to tell for sure that the Moore display isn't history or art is because we know Moore's intentions. Such intentions should however be irrelevant.
But back to your point. Isn't it a bit like claiming the SC is only partially pregnant ?
The various displays of sculpture in the SCOTUS building are meant to honor the various sources, development, and effects of law in history. You can read about them yourself here, here, and here.
The North and South wall friezes contain the largest number of actual personages (as opposed to allegorical figures). Only 3 of 18 are religously oriented. Confucius is referred to as a philosopher, not a religious figure. And I was wrong; while Moses and Muhammad are depicted, Jesus is not. Odd, for a Christian nation, don't you think? Perhaps no one saw room for the Great Commandment in American law....