okay so I'm gonna become one of *those* users but this is the sort of thing which is worth sticking behind a content filter and IME it doesn't reduce engagement, if anything it increases it because people are more likely to boost if their instances are pretty strong on putting the filter up. Sounds counterintuitive but it seems to hold up.

seconded. Think of content warnings as respect and consideration, then it's not counterintuitive anymore: people prefer boosting considerate posts over inconsiderate ones.