If I were to guess, the one of these that has by far the most impact is the Google featured snippets. There's constantly a tension between Google and online publishers about Google wanting to serve people answers quickly (with "on the search page" being the fastest version of that), but that not actually helping the publishers.

I couldn't agree more about the toxicity, though. I don't pretend to know much about who's right in the Stack Overflow vs. moderators debate, but every time I visit an answer on Stack Overflow and glance at the right sidebar I feel like a kid who's just walked in on his parents fighting. The tension between the company and the community is palpable and it makes the site feel like an icky place to be.