Of course it's fucking sufficient, that's literally the definition of "legitimate interest" [0]. I write comment. I want you to publish comment. You publish comment, and don't spam me - maybe even don't require my email.
If you say, "hey, provide your email, and I'll send you newsletters and you can unsubscribe at any time", and I say "sweet, sign me up", and then you only send me newsletters with no tracking or adtech, that's legitimate interest.
If you use a third party, if they store only the minimum necessary and don't use it for anything else, that'd be fine to. E.g. obviously they need my email address, but only for sending the emails.
And if Mailchip were decent, they'd just send out plain emails. The problem is probably their emails are full of tracking links and other adtech garbage, and who knows who they sell info on to?
Then again, they call themselves a marketing platform, not a newsletter service, or email sender. Kind of obvious.
Also, that's a shitty dialog. Mailchimp's private policy and terms are probably largely void under EU law anyway, just by being almost incomprehensible by the lay person. How am I supposed to give consent freely when it would take days to read? Probably best to avoid Mailchimp. Thanks GDPR!
Edit: ordering
[0] https://ico.org.uk/for-organisations/guide-to-the-general-da...