I agree with the OP in the fact that MailChimp's simplicity can render it lacking.
Yes, it is user-friendly, but in my opinion, it is user-over-friendly in that it feels more aimed at users without any marketing/technical experience at all in the same way that a Wix website is good, but not for a marketing/design professional, as the OP is.
Of course, the ideal solution is using custom coded email templates, but that goes in completely the opposite direction and becomes over complicated, and requires a lot of technical know-how.
If you are looking for a happy medium, one that gives you enough flexibility to build and design emails as you see fit without the tight constraints of MailChimp, but without having to entirely custom code them, then a good option is MailJet (not affiliated, just a customer). It has a user-friendly drag-and-drop style editor for ease of use, but that editor allows you to easily edit settings such as paddings and alignments without having to touch the code.