I think it's short sighted to say google is killing individual sites rather than changing things algorithmically.
Let's say you wanted to kill these sites, how would you do it?
- Reduce the value of domain authority. Just because a domain has 11ty billion pages and 11ty billion backlinks across those pages doesn't mean an individual page with no backlinks has any real value just because it sits on that domain.
- increase and/or rework the duplicate content penalty so that content spread over many many sites (directories) gets an even bigger penalty than content duplicated fewer times
- kill the domain authority of domains with a large percentage of duplicate content
- kill the domain authority of domains with a large percentage of engrish/spun content
- kill individual pages or domains that are getting poor click through rates from search results. People don't click on these sites, so reduce their value based on these clicks
This can be done algorithmically.
The whole reason google can't stay ahead of us is because they have to do things algorithmically. They can't just kill one type of link, profile links, links from an individual domain, forum links, blog comments, etc. The very links they need to kill most are also some of the most valuable when they aren't spam. Forums for example are full of really high quality links to sites with great content. Blog comments when they aren't spam, link to active bloggers who write original content.
Google is google because they use backlinks to determine search rankings. They can't ever change this, and because of that, building backlinks will always work as long as you're producing quality and those links look natural.