They may be mixed up but a distinct type has clearly arose in rural england (and in many places), and something has shaped it. All the dog breeds are mixed up too, but still you can say this dog has long drooping ears for this or that reason. Even dog types, which aren't breeds, that arose recently for a purpose will lean towards distinct similar phenotypical characteristics. For example in australia we have "pig dogs" which are mongrels used for hunting wild boar, even though all and any breed can be in the foundations for the pig dog strains, in the blackberry country of central new south wales (for example) where there is lots of thorny brush the pig dogs will tend to have small beady eyes, and obviously it's to minimise the chances of getting them injured on thorns. There are countless similar little cases all across the country, and all across the world of dogs.
Humans are no different. Even modern strains like "midwestern americans" or haitians have distinct phenotypical tendencies. The fact their foundations stem from mixed ethnicities is neither here nor there. It's not like "they're randomly whatever because they aren't pure", they aren't whatever, they're something in particular. Who can't differentiate between an english farmer and a dutch hang-gliding enthusiast? I can, and it's because they're from seperate breeding populations, not through the eternity of history, but long enough for distinct types to deviate from one another.
