a) as that of Man o' War , who won
b) not unlike that of Man o' War, who won
Between a and b , b is better because we are comparing two nouns, the speed of one horse with the speed of another horse. But ‘like that of” would have been good enough for that purpose. Why the author chose to use two negatives to make one positive is somewhat bemusing. But more importantly, the use of ‘who’ to refer to a horse is indeed perplexing.
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