As you suspect, AWS does not intend Cognito to do mail-list management; only transactional emails.
From what I've seen, it's pretty common to manage mail-outs (including product updates) through something like MailChimp or HubSpot, which include additional tools to track user engagement, manage campaigns, and handle the various data protection requirements that different regions expect of companies.
That said, for relatively modest numbers of users (think 100s) you can get away with using ListUsers with a lambda and SES.