About Mailchimp being dead, not anytime soon. SMTP providers have been there for over 10 years now. Amazon SES is just one of them. I think what makes email marketing platforms like convert kit business model so successful is the simplicity, branding, and good marketing. You recommended Sendy and MuxEmail, instead of going with this subscription-based softwares why not go with a free open source platform like mautic that offers way much more.