> Alzheimer’s isn’t my field, but I got very interested in it, spent six months studying the literature, and came away believing the amyloid hypothesis was basically completely solid.

If the accusation is "the field has been captured by a group with a vested interest in a model based on fraudulent research, strongly biasing what gets funded and what gets published" I wouldn't expect "studying the literature" to be particularly helpful in assessing the claim. It's sort of like saying "I read all of Enron's press releases and SEC filings, and they sound legit."

The defense reads more like a special pleading or sunk cost fallacy. There has been a lot of research done on one hypothesis, actively excluding alternatives, so that hypothesis deserves to be considered until disproven (he does, iirc, allow for a test that would de-privilege the amaloyd hypothesis).