I hadn't realized they screwed up the Sussex line as well
Hepburn doesn't mention Sussex. He has Immigrant William coming straight out of the Yorkshire family. Who are still of interest because other immigrants did - John Clayton the attorney general of VA and his son the "father of American botany".
For William, Hepburn goes with the memoirs of Judge TJ Clayton, presumably a descendant. Looks like the judge had investigated, and not found anything, and handed down his verdict with authority even though he was making it up.
The judge had Immigrant William as the son of a Thomas who was the heir to Clayton Hall and was a son of William of Oakenshaw.
Hepburn figures the judge has garbled it, though he isn't rude enough to say so. He decides there were 2 Thomases who were cousins. It was Thomas son of John who was heir to Clayton Hall.
But he also shows a Thomas of London who is the son of William of Oakenshaw and the father of Immigrant William.
What isn't yet clear is, how he knows Thomas of London existed, how he knows he came from the Oakenshaw family (he's not in the published charts), and why he makes the immigrant the son of this Thomas and not the other one (since there's obviously no evidence, because he was neither).
But often one thing leads to another. On WikiTree, although William's alleged son Thomas, known only from Hepburn,
has been unburdened of the Penn line, he's been claimed as the ancestor of some Brashers.
Looks like William B Brasher married an Elizabeth, daughter of a Thomas Clayton. Nobody has a clue who he was, so the internet is making random stabs in the dark.