I get maybe one genuine spam not marked as such and maybe one false positive per month.

I'm getting a lot of emails and between 10-20 spams a day, but that's years of the very careful messages reporting and categorisation.

Similarly with important and "normal" emails - i only get one-two important per week, and marked as such for the same reasons; no false negatives.

It's not just you. I experience the same thing. It is thoroughly maddening.