It’s pretty clear from the failure of the antibody drugs (the ones that end in 'mab’) that suppressing amyloid doesn’t work - and it’s not clear that those plaques are causal. Ditto tau, which could easily be a result - not the cause - of neuronal death (neurons have long structures internally for transport proteins to drag energy bearing molecules one way, depleted ones the other; the cascade involved in carrying a signal is energy intensive and mitochondria are in the cytoplasm near the nucleus).
Of course, it could easily be the case that once MCI is diagnosed, it’s too late. And that’s who those drugs are being tested on...