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.
Do you have any awareness of how tacky this sounds?