If someone had suggested romans-> normans-> british, I could have understood that, except the normans aren't an exploration age civ really. If we had a medieval age then I think that they would fit perfectly....but Ed Beach had his heart set on the Normans, so Normans we get.
(And as far as invading dynasties and emoires from outside not counting, then China (foreigners Qin don't count) and India (foreigners Mughals don't count) don't have full representation, so I will laugh at anyone who claim to want a full Anglo-British "like China" but refuse to count the Normans, or even the Romans for it).
Looking on the 2k Web site, I can't agree that the civ 7 normans are '100% english' either, they have some English elements, but other elements that are clearly French.