The decline and fall was within a lifetime. Not just a random person's lifetime, but that of a single famous individual. By any of the usual endpoints (Indian Independence, Suez Crisis, Winds of Change/South Africa's withdrawal from the Commonwealth) the Empire ended while Winston Churchill was alive- he was born in the 1874, at the height of the Empire, graduated Sandhurst and joined the British Army in 1895, took Queen Victoria's shilling in several colonial wars, then was Secretary of State for the Colonies in the 1920s, and died after Britain had withdrawn from most of her African holdings.

Within a lifetime or so, which is certainly within a range you would expect for a global empire to collapse; that rarely happens overnight. That said, it is an unfalsifiable supposition, as much as the article's supposition is, although I framed mine in less certain terms than the article claiming it as factual that said elites were effective.