As a spammer, you've got to assume Google's going to catch onto your first three million fake accounts and mark both those accounts, the email servers' IPs you use to send, and the email list itself as spam. Consider your first three million gmail account burned by that point.
The less obvious second phase then, using your next three million fake, aged, but-with-fake-email-traffic-to-make-them-seem-real Gmail accounts, is to sign up for not-spam newsletters, but mark those as spam. The wishful-thinking hope is that with enough of those marked as spam, the wider public will see more articles like the linked article, and ever so barely push back on Google, who then have to figure out another way to distinguish signal from noise in a vastly complicated and ML-enchanted algorithm.