But in idiomatic spoken English, at least in the US, people omit that have. I agree that it's there for more formal or more British English. Also, what you're

But in idiomatic spoken English, at least in the US, people omit that have. I agree that it's there for more formal or more British English. Also, what you're describing goes beyond native level English and reaches the level of professional writer/teacher/linguist/editor/etc level English. I would expect many HN readers to have English proficiency beyond native level.