Nothing will ever ruin email. A private email server, or a federation of mutually-whitelisting ones, is the ultimate social media, and not at all a bad personal information management system too.

Edit: typo

I hardly ever see any spam nowadays, happy fastmail user.

spam filters are effective at dealing with that

Not in my experience.

My self-hosted email filters too little spam, while GMail etc filter too much (e.g. important company correspondence leading to orders almost being lost because they landed in our GMail spam).

Does GMail silently filter spam now? I get maybe 5 new messages in my spam folder per month for the past couple of years and I'm not sure if Google is just dropping the most blatant spam or if my primary address is somehow not on any lists.

It works both ways right? If you self-host you are seen as the spam.