Any of the great 19th century historical novelists could have pulled it off. Tolstoy, Scott, Thackeray, Cooper, etc. Mark Twain would have turned it into a farce or a satire. Washington Irving would have handled it with a deft touch. Disraeli would have tried it, but would probably have produced an overly extravagant scenario. H.G. Wells did write an alternate history novel, the unfairly neglected Men Without Gods, in which he was the first to use paratime travel as a literary trope. Robert Louis Stevenson, with his profound grasp of politics and his knowledge of engineering and of Scottish history (and later, of Samoan oral history and politics), could have done it well. Probably Kipling too. Of mostly 20th century writers I'd say Margaret Atwood, Marge Piercy, F. Scott Fitzgerald, John Dos Passos, Alexei Tolstoy, Dmitri Merejkowski, John Le Carre, Robert Graves, Somerset Maugham, George Orwell, and Aldous Huxley all would be, or would have been, good at it.
Among today's popular writers I'd like especially to see Laurie King (creator of the Mary Russell-Sherlock Holmes series) try her hand at it. I'd also like to see s-f writer John Birmingham move beyond ASB scenarios and attempt a realistic POD alternate history.
Among 20th century political figures, Winston Churchill wrote a very clever alternate history short story about the U.S. Civil War, and I'd guess Teddy Roosevelt and Eisenhower had the ability to devise elaborate alternate histories of modern wars. Any of these three would probably have needed a co-author to add characters and dialogue. Trotsky could have done it without a collaborator.
Among pre-19th century writers, it would have been wonderful to have an alternate history of the English Civil War written from exile in Holland by Margaret Cavendish (1623-1673), Duchess of Newcastle, and her husband, who was the top royalist general and also a person of literary ability. The Duchess wrote the first explicit alternate world yarn (with a portal between that world and ours), which her husband praised in a notable sonnet, so they would have easily taken to the idea of alternate history if given a model.