I disagree, I get plenty of spam from Mailchimp. Spammers seem to be able to add email addresses to Mailchimp without verification, and they just keep making new accounts/"campaigns" to re-add my email addresses.

Legitimate companies like to not provide the legally-required opt-in flow and assume consent without ever enabling or disabling a consent checkbox. That is spam too.

It's on Mailchimp to not take business from companies that abuse their system. If they get flagged as spam and their other customers have delivery issues because of that, I see that as a feature, not a bug.