It is a product of its time but it does represent an attempt by the Latin churches in the United States to re-write American history and re-define American [Catholic] identity.
The procession of saints includes, among others, St. Juan Diego (the first canonized male Native American), St. Kateri Tekakwitha (the first canonized female Native American), St. Teresa of Calcutta (an honorary American citizen), St. Francis Cabrini, M.S.C. (the first U.S. citizen to be canonized), St. John Paul II (the first pope to visit the National Shrine), and St. Junípero Serra (declared a saint by Pope Francis at the National Shrine in 2015 for the first canonization ever to take place on American soil).
Is there a single political entity that is the United States? That is the nationalist myth that arose 1865. Then again, only a basilica built in the seat of the Federal Government would pretend to be a national Catholic symbol. And then there is the inclusion of two modern popes...
As for the quality of the mosaic itself -- I don't think it looks very good, but it goes well with what else has been installed in the upper basilica. The depiction of the Most Holy Trinity is uncanonical; did the artist not consult anyone traditional authority on this question? The figures themselves look like the "naturalistic" representations of saints that are done in modern stained glass windows -- they don't look like mosaics at all. Maybe it's because of the distance and the resulting resolution, but I think the mosaic loses something as a result. As for the representation of the "Immaculate Conception," I find that I cannot relate to Western depictions of the Theotokos these days.
Then again, that sort of ambition and desire to create such a large mosaic for a very large temple reflects the triumphalistic hubris of the American [Latin] Catholic Church, which didn't go away with Vatican II. "This was the best they could do, and they thought it was great?"
Perhaps it is a good thing that the Greeks didn't attempt to recreate a version of Hagia Sophia on American soil.