How hard would it be to assign websites an actual reputation again?
Include ads on the destination website as part of the reputation score. If a website is loaded with ads, sink it to the bottom. Google doesn't do this because they likely make money from the ads.
Heuristically determine spammy content. It's pretty easy to tell at first glance which content is bullshit, so it's probably not hard to create an ML model to do the same classification.
Manually assign positive weights to websites used by engineers and domain experts. You could even curate this list in the open and solicit help in maintaining it.
it seems that the web has for at least a decade already been at the point where a search engine that is built to be useful by humans should (ideally, but apparently impossible with the current skewed incentives due to ad business considerations, overheated stock market, over-enthusiastic ML expert workforce, etc.) index only sites that opt _in_, vetted by humans.
there is a clear upper bound on the amount of total legitimate web content, and that upper bound is not prohibitively high -- linear on the total number of coherent-content-producing humans with only so many hours in a day and only so many years of adequate brain functioning (and not on the amount of whatever computing resources that are thrown in to support whatever algorithmic content fire hoses that the currently-dominant search engines contend with).
That wouldn't take care of SEO spam, which is very good at stuffing its pages with whatever words people search for.
Also, as much as I hate to admit it, Google is pretty good at guessing wrong spelling or synonyms and getting good results in a majority of cases.