Correct me if I am wrong. there are already treatments discovered for removing plaques, but it turned out that plaques aren't the real cause of cognitive decline. That's what I read before.
However, that doesn't mean removing the plaques will replace cognitive abilities.
If you think of neurons like plumbing, the plaques clog up the tubes, and the neural connections are no longer firing. Removing the plaques doesn't mean a whole doesn't exist in the tube, it just means you've unclogged it, meaning the contents can now spill out.
This isn't to say that amyloid plaques are the only marker in age related cognitive decline.
My suspicion (and I do some work in the field) is that many different diseases are being lumped into a single thing that we don't completely understand. There is a lot more which will be learned in the next decade.
There was a research scandal a while back that called into question some amount of data. And there’s the fact that many attempts at attacking the plaques have not been able to show any significant improvement to patients.
You're also mostly correct that attacking the plaques have not shown significant improvement.
But that only shows that the damage done to the brain is irreversible - if in fact the plaques are the cause/related. It does not show that preventing the plaques/damage is the key.