If he is in Europe he can probably force Google to allow him to download his data under GDPR
It's been the case before GDPR that you had to at least threaten legal action to make corporations behave. Freedom of association does typically mean that a human can just ban you from ever being their customer again, but that's IMO an important freedom. The monopoly ISP in your municipality doing the same to you does not seem ok, however. And it might not be reasonable to ban ownership of a Google account that's used exclusively for "Sign in with Google".
Then it is unrealistic to expect that an average individual will have money to sue the data processor, as the cost is out of reach for most of people.