FastMail uses SpamAssassin, and I get less than one spam emails in my inbox a month, with essentially zero false positives (which is the tricky bit where gmail seems to fail – I'd rather have the occasional spam in my email than false positives).

In short: you can probably do better than 3-5 spams per week with SA.

The big problem is the entire thing is a beast to configure with all the documentation of a Babylonian cuneiform stone tablet.