I guess you could say it that way. When some researchers say plaque is a "symptom," they might just mean that there is an underlying mechanism that is broken and causing plaque to build up. No one thinks the plaque is good or normal. The real question is why some people get it in the first place and others don't.
By analogy, broken bones are a symptom of osteoporosis (chronic brittle bones). No one is saying a broken bone doesn't hurt or shouldn't be fixed, but we've had more success historically by ALSO treating the underlying cause to prevent damage from coming back.
No, he's referring to the fact that some researchers have questioned the mainstream adoption of the amyloid/tau hypotheses -- that the plaques and/or tangles are the cause of the dementia.
It's mainstream, but it is not proven, and there have been some studies that cast at least a little doubt on them.
So the OP isn't using an off-the-wall phrasing, it is very much a question of whether the plaques and tangles are the cause or the effect of some yet-to-be-established mechanism.
There is no better phrasing.
This makes it clear that the mechanism is still a matter of hypothesis:
Anyway, the apparent success of the ultrasound does indeed seem to be evidence that the plaque/tangle hypotheses are correct in assuming these things to be causal and not merely correlated symptoms.
By analogy, broken bones are a symptom of osteoporosis (chronic brittle bones). No one is saying a broken bone doesn't hurt or shouldn't be fixed, but we've had more success historically by ALSO treating the underlying cause to prevent damage from coming back.