I’d challenge that definition. 0 spam messages are a solved problems, any positive integer greater than zero and it’s still a problem.
Yes, we solved it by centralising and ceding our power, so that two companies can see when a lot of people get the exact same message, and delete it for them.
Not at all. I never had a google account and I know many people who do not have one, and no, they have no problems with spam either.