Gen.Mannerheim
Grand Moff
I don't think that's entirely fair. His argument, as I understood it, is that quibbling over the reality of Arthur misses what's genuinely interesting about the period, and that historical records should be read with more attention to what they say about how people in the author's time thought about themselves and their historical context, rather than trying to build elaborate shoestring-theories. It's more than just a long-winded "i unno".
That said, I do think that Halsall muddies his own point by spending too long engaging with pop-historical discussions of Arthur, devoting enough of the book to them as to make them seem in-themselves important, and allowing the "agnostic" interpretation you're making. The historiography of Arthur could be a useful way of making a largely-overlooked period in British history accessible to non-scholars, but Halsall lets them take up rather more of the book than is necessary. You definitely get the impression this is a guy taking an opportunity to grind a few axes.
(I can't comment on grave goods, because my historical education is exclusively Early Modern, a sub-discipline in which written records are plentiful and archaeology is a form of witchcraft.)
That's kinda what im trying to say. The book was marketed as a true historian's look at Arthur, and Halsall himself states that the genesis of the book was his annoyance with pop history domination of the subject. He doesn't really explain his point about Arthur being a better launch point than the destination until the end of the book, making the migration sections really confusing for those here for "Arthur"
From what I understand, this is his harshest reviewed book. Historians blasted it for taking potshots at larger topics, and casual reviews are mixed for the above confusing reasons.