All this is interesting, true, and useful. However, at the level where one is dealing with a WikiTree profile containing very little information, uploaded by Gedcom 5 years ago and touched on very little sense then, whose primary source is an ancestry.com user-submitted family tree with no indication of further sourcing, and one finds an Anglo-Saxon monarch linked to his father with a Welsh patronymic form, one is faced with a choice:
1) The profile, while unsourced in virtually every other way, embodies a sophisticated understanding of the complex relationships between early Anglo-Saxons and their Briton neighbors, or
2) The profile, which demonstrates a significant lack of interest in actual facts or sources or how things were done 1500 years ago, is consistent in reflecting a lack of attention to naming patterns.
I think the principle of "Occam's Razor" tells you that when you have to guess between two alternatives, the guess which presumes the simplest explanation is more likely to prove true...