Why Coronel ranked as an exceptional British defeat

Was Coronel really Britain's first naval defeat since the early nineteenth century?

No, but its total losses and casualties made it exceptional in scale compared with the intervening defeats.

The Royal Navy had lost ships and squadrons before Coronel, including actions during the War of 1812 and defeats on the Great Lakes. The correction matters because a claim of no intervening losses would be plainly wrong. The intended distinction rests on the totality of the disaster and the number of men killed. Coronel was the most significant British naval defeat of comparable scale for roughly a century, though it was not literally the first British loss since the Napoleonic era.