I think you've probably got it right in suggesting that at mostlingering memories of Alfred were grafted onto the already existing Arthur legend . To the best of my knowledge there is no mention of Arthur in extant pre- Conquest Anglo- Saxon literature - hardly surprising since the Anglo Saxons were an illiterate society at the believed time of Arthur - the 6th century.The 'real' Arthur was hardly someone likely ever to be celebrated by the Anglos Saxons.

The Arthurian tradition, in the form that we recognise it , was mostly a french import - through the works of, for example , Marie de France and Chretien de Troyes.Its interesting to speculate how it took on its essentially english character - lingering memories of the line of Wessex - especially Arthur seems to be a reasonable suggestion.