The Siamese is significantly different in size, shape, and attitude. So are most of the "oriental" breeds, but I bred and showed Measers for 15 years, so that's the one I know best.
And the British cat breeders of the 1880s-90s are the ones that 'fixed' the type (i.e. established a blood line that would breed true to type).
Anybody who has much to do with the Measers will tell you that they are different from other cats.