Well, England did not exist before the 11C, there were various tribes but there was no 'nation'... before that the peoples would more accurately be referred to as peoples of Briton, as in people who lives on those Islands termed British.
This is not true. A “nation” is not the same as a state. For example, there has been a German nation for centuries, which was recognized as such both at the time and by later historians. However, Germany only become a united state comparatively recently, in 1871.
The question is not when the English state was founded but when English civilization began. It is commonly dated to the fifth century, which is when the first English settler units stopped wandering around the map and went plonk in southern England (so to speak).
England was already a flourishing civilization by the time it was united. In particular, the adoption of Christianity was landmark in the development of English identity. From the Encyclopedia Britannica:
it is important to notice the religious conversion of the people we commonly call Anglo-Saxons. It began in the late sixth century and created an institution that not only transcended political boundaries, but created a new concept of unity among the various tribal regions that overrode individual loyalties.
England was eventually united under one king in either 828 or 924, depending on how you define it. But the English were a civilization long before then.
As far as “Britons” is concerned. This term refers to people who lived in Britain before the Anglo-Saxons arrived in the fifth century. It certainly doesn’t refer to the dominant inhabitants of England in the period 500-1000, as you imply.
There is a simple reasons why “Britons” is no good as name for the civilization based on England/Britain. They did not create this civilization. They were part of the ancient Celtic civilization, which did not last beyond the Romans.
I can guarantee you that if a British Empire civ didn't include Irish cities, you'd find a ton of Northern Irish Unionists on here complaining about it.
Yes, only Ulster Unionists would have something to complain about. But not citizens of Eire.
Really we're only talking about one northern Irish city, Belfast, which is potentially big enough to get into the game. But the cities are pretty arbitrary anyway. (If they the same as in previous verisons. Unfortunately I don't have the game yet). Hastings and Canterbury grow into giant core cities. Manchester and Birmingham are tiny outposts. So I guess lots of people could complain that their particular city isn't included when it should be.
EDIT I notice that the German cities list includes Koeningsberg, Danzig and Graz, none of which are even in present-day Germany. So no one could legitimately complain about Belfast as a British city historically, which it certainly was when it was founded (in 1603 by Sir Alfred Chichester, apparently, for English and Scottish settlers). Not that I'm advocating inclusion of Belfast. I'm quite happy with an English civ.