Not sure if you are actually developing the emails or not, but from a front-end developer's perspective, I hate to touch my email templates codebase because it has to be coded in certain way that works with the email provider.

I cannot see what the end result is going to look like until I actually send out a test email and see it in my email clients. This DX indeed feels like 2010 if you compare it with today's DX for developing websites.