[tokenadult]

Insiders subtract the false or useless bytes (an action easily captured in statistics and then maligned on the internet by pundits), but also look at the true and useful bytes, fact-check them, and then leave them in place. This contribution --- curation --- is not captured in any statistics. . . . Unfortunately both sides' conduct may be scaring away the people who are actual experts on those long-tail topics.

Correct. But not just long-tail topics, but any topic that can only be properly treated by deep immersion in the subject, and especially any topic that is controversial. A lot of point-of-view pushers on Wikipedia do a lot of their POV-pushing by "framing," just making sure that some wikilinks to articles they like persist, while others are deleted, or that navigation templates or article categories play up the articles that best represent their point of view. And that's before we even get to the issue of deleting reliable sources.