If you manage your domain and point your mx at google, and some ai decides your drive contents look bad or some non-official youtube app violates some api access rule and they kill your whole account, you just point your at any other service provider.

That will be an annoying few days, but you don't lose anything too important. Maybe for a day or so you can't receive password emails, but you will, just after the switch shakes out.

In the mean time, you're enjoying the convenience of a big mail service, and playing the odds that it's probably not going to happen to you, and it's ok to live with that risk because if it happens, it's just an inconvenience not a disaster.

As for losing old emails, I use thunderbird on my laptop, and that ends up getting a copy of all my gmail even though I also read those same emails on my phone. If google kills my account, I still have all my old emails even without my own domain.

I don't know if google even offers domain regisration to individuals, but if they do, I just wouldn't use them for the registrar. All other services can tolerate that risk as long as you use someone else as registrar (namecheap is good).