That's actually the reason why I use Gmail instead of switching to a smaller email service - it's "too big to fail," I don't think Gmail will be discontinued for as long as Google exists, even if it became somewhat unprofitable, due to the outrage and class action lawsuits that would result.

Hosting yourself is a good way to have half your sent emails never arrive.

Own the domain name, but let one of the big players handle deliverability for you.

This. I use my own domain names with gsuite and protonmail.

Hosting an email server in these days with DMARC, SPF, DKIM and all those mail filtering blacklist is is world of pain but that's the price to pay for reduced spam I guess.

I wish there was a modern protocol equivalent with authentication builtin.

Paying for it has its risks as well. If you are unable to access for an extended amount of time (injury, travel, etc) and your payment method becomes invalid, it could cause your account to be shut down.

This is a valid concern. I would pay for a year in advance at least.