> It's mostly a time delay, since the alternatives to verify your identity seem to be a different emailaddress or a phone number and then you're back to square one imo. The phone number is still susceptible to social engineering and the alternative mail likely is too. Ideally I want something where keys gone = account gone.

I can think of options less extreme than keys gone = account gone that are still very secure.

e.g. To enable "Extra Advanced Protection" you have to visit Google HQ in your region, where your DNA is sampled. If you ever need to recover your account, you have to visit Google HQ again for another DNA sample, after which you're provided with account access, in person.