Yes, on that point I agree. Grammatically, "built" is fine but stylistically another word would be better.The Acropolis is a hill in Athens, not a building.
I disgree with the Newt on this. For me, "...the greatest building to have been built" is not great, but it's preferable to "...the greatest building built". We avoid using adjacent words with the same root (They
builterected the building. She drives up the drivegravel path.)