This article really confuses what AWS is (IaaS) as to MailChimp (SaaS). Sure you can spend months building a tool where you keep your registered newsletter subscribers with their contact info, and create good looking email templates, or create an automated scheduler to send those 100,000 emails in bursts because even SES has a throttling limit.. But do you pay for the extra service or build it and maintain it yourself? You might need to pay people more money to do that than what you pay for MailChimp.

Maybe MailChimp uses AWS SES behind the scenes? Have not checked. SES is a service for email delivery. It is not an email marketing software.