But it is the Temple of Concord that is the best preserved Doric temple in Sicily (if not the world), thanks to its subsequent use as a church in the sixth century a.d.
The Temple of Concord is the least well preserved Doric temple in Sicily. 
mnli hypothesis: The Temple of Concord is the least well preserved Doric temple in Sicily.  premise: But it is the Temple of Concord that is the best preserved Doric temple in Sicily (if not the world), thanks to its subsequent use as a church in the sixth century a.d.