Did someone try to remove amyloid plaque from the brain of an Alzheimer's patient and see what happens? I've heard of studies that disproved the amyloid theory.
Yes, removing the plaque has been tried and has so far been unsuccessful at improving Alzheimer's.
The way I picture it (and I'm not an expert, still learning about this stuff myself) is to look at amyloid plaque as a clog in a pipe between nerve cells. Now picture the blockage putting a crack in the pipe. You can clear the blockage, but you still have a cracked pipe, so anything you send down the pipe will spill out.
We have no way of fixing the broken pipe, so we must prevent the build up of the plaque in the first place.
https://clinicaltrials.gov/ct2/results?cond=Alzheimer+Diseas...
The amyloid hypothesis is of course disputed, but largely because stopping whatever causes plaque formations could prevent or lessen the impact of Alzheimer's has proven so difficult and would ultimately provide little benefit to those already suffering with the disease.