Before Wiz or anyone else at Paradox moves Wales/Welsh into the "British" Cultural group I think they should know what "Britishness" or to be "British" means .
Welsh politician Gwynfor Evans said of Britishness, "Britishness... is a political synonym for Englishness which extends English culture over the Scots, the Welsh, and the Irish".
"Britishness" is a modern concept that is usually used after the acts of union by politicians to try and create a sense of British identity, particularly by modern right wing parties. It has become synonymous with English due to the English political dominance and the recent rise of Welsh, Northern Irish and Scottish nationalist parties who want to create a separate parliament for their countries and therefore need to undermine the existing UK (British) parliament.
The fact that you are quoting a president and first MP of Plaid Cymru, a party whose purpose is to gain autonomy for Wales and encourage a national identity, who was politically active during a turbulent time and who wrote some VERY nationalist books, I feel highlights my point.
To paraprhase to be "British" has become a political term, it's no longer linked to the Welsh and the Cornish who take their ethnic and linguistic heritage from the original known settlers from what I believe Romans called Britannia aka the Britons peoples. It is a term of domination of the English over the "Celtic" peoples and the general eradication of their languages, cultural identities and right to rule themselves, and to some though certainly not all Welsh, Scots or Irish being called "British" can be deemed offensive..
"Britishness" is not the same as "British", "Briton", "Britain" or "Britannia". One is a politically loaded term used by politicians for political goals, the others are names for the people and land of Albion, names from the original Celtic that were then Latinised by the Romans. The word "Britain" is used in the first recorded (Greek) texts as the name of our Island(s).
In terms of "domination and general eradication of language and culture", it was the English Kingdom, before there was such a thing as Great Britain, who attempted to eradicate the welsh language and conquer Scotland. It was during the English civil war that they attempted to do the same to Ireland. I will also remind you that it was a Scottish king who came to power in England, not the other way around, England had not tried to conquer Scotland for a while by that point.
As for some sort of Ethnic difference between the "English" and "Celtic" peoples, that has been disproved by genetic studies. The English are 70-80% the same people as the Welsh and the Cornish are actually ethnically more similar to the English than to the Welsh. They are all still the same original Brittonic peoples who settled the lands, with varying amounts of European influence.
In the 2011 Census people in Wales for the first time had the opportunity to describe themselves as Welsh (2011 shocking eh) which the majority did as Wales is obviously the home of the Welsh, only 10% of those stating they were Welsh also chose to identify themselves as British..
2011 was also the first Census where people in England had the option to describe themselves as English. They were both absent as an option from the 2001 census and the same campaign to make Welsh an option was also about making English an option.
58% of people in wales described themselves as Welsh only. That is SMALLER than the percentage of people in Scotland who identified as Scottish only and the percentage of people in England who voted English only (both larger than 60%). Whilst only 10% stated they were Welsh and British, almost 20% were British only and over 10% described themselves as English. In fact, Wales actually had the same proportion of people who identified as being British as Scotland and England (only London has any sort of difference from the rest of the country).
Stop trying to quote out of context statistic, according to the census data there is no such thing as British being the same as English.
Wales in 1444 has no place in the same cultural group as the English we were vastly different peoples and "British" as the political term didn't exist then and the cultural term had nothing to do with the English. Owain Glyndŵr's rebellion from English rule and temporary de facto independence where French forces landed in Wales to help out (never represented in previous games 1400 start sadly) was still in living memory..
The cultural term "British" has everything to with the English. The political term didn't exist because no one had come closer to controlling the entirety of the isles.
But quoting a political rebellion means nothing, no one is arguing that Welsh stop existing as a culture or that they liked each other. There are plenty of same culture group cultures that dislike each other.
*An adequate culture name that describes English, Lowland Scots and Americans is difficult, British doesn't make sense for multiple reasons, Anglo or Anglo-Saxon may offend modern day Scots but is perhaps accurate for Lowland Scots there was a good post on this earlier in the thread and Americans though mainly from Anglo origins during this time frame are multi-cultural.
Anglo-saxon is offensive to modern day English people as well. It is a bit like making English part of the French culture group.