Wales wasn’t conquered by the Anglo Saxons. They were subdued by the Normans. Glastonbury and King Arthur are false creations borrowed from Welsh history, and are a tenth century propaganda exercise.
The Welsh took over England when the Tudors took the throne. The Red Dragon finally defeated the White Dragon.
The real history has been obliterated. The Dark Ages were not dark at all. The history is still possible to research. The history of Britain as taught in schools and universities is entirely wrong
The Blood Of Avalon by Adrian Gilbert.