I don't think your definition of spam matches the one that I understand it to mean. Spam is random email from someone you have not had contact with before firing messages to every address they can find anywhere on the web, the dark web, etc. Or if you ask not to be added to a mailing list and are added anyway. They often use fraudulent tricks to try to get the email through filters, such as fake from addresses.

Spam is not email from legitimate companies with valid contact details that have an opt out that you forgot to click when you signed up with them. That's legitimate marketing emails. You might argue they also shouldn't exist, but they are a different category.

I get plenty of the second from mailchimp (it's what they do), almost none of the first. Marking the second kind as spam, rather than clicking the unsubscribe link is dangerous because it teaches your anti-spam filter to reject messages from legitimate companies. You might find that if they need to contact you for a genuine reason e.g. a reciept for a future transaction, the message is blocked.

No, it's valid for me, and I just verified. In spam filter for past month: 0 mailchimp. In valid emails: 6 emails from a service that I signed up for via mailchimp.

Checking my received emails for mailchimp I see a whole bunch of legitimate emails, including for flightschedulepro which uses it. I also see replies to my abuse reports to mailchimp saying the problems have been addressed.

Do you report any of these spams to mailchimp?

Indeed, Mailchimp is a tool specifically built and advertised to send spam.