I have used both, and I agree with your analysis. The great thing about MailChimp is that it lets you see the email in different clients. That is really the hardest thing about sending emails. However, you can use that service without doing everything else through MailChimp. Also, once you get the hang of it and develop templates, it no longer is much of an issue.
What I like about Mailchimp is that you can setup autoresponders such that only a subset of your email list will receive your follow-up emails based on when they signed up for your newsletter. For example, if I only want recent subscribers from the last month to receive one of my autoresponders, I can simply specify this using MailChimp’s autoresponder interface.