I have Fastmail and Google email addresses which have been active for over ten years each. The Google account sees several emails bypassing the spam filter every day and, worse, several ham mail being flagged as spam each month. Fastmail, despite that address being more exposed (it's my own domain name which I have used for over twenty years) and having higher overall traffic, sees maybe one or two spam a day hitting my mailbox and only one or maybe two ham to spam a month. I don't get where Google reputation for good spam filtering comes from. It's barely passable when it comes to detecting spam AND ham mail.

You're arguing that Google had great spam detection and I agree. My point is that it's gone noticeably downhill since then.