The victors always rewrite the history
The old saying goes, "the winners write the history books", but the actual fact is, the history books write the winners -- and that's the attempt being made here. There's nothing but a few artifacts found, and the ridiculous claim being made is that it completely rewrites the contemporary sources, which were A) not published at the time, and probably unknown outside the writers' ivory towers, and definitely not written under some kind of royal commission; B) Alfred needed a reliable ally to resist and eventually expel the Danes, and replacing the mighty king of Mercia would appear to have made no sense; also C), the country wound up called Eng-land, not Sax-land, showing the importance of the Angle kingdoms during the time of the heptarchy.