20MB of inscrutable JavaScript allows you to have a) a sane structured component system where you can actually build up UIs compositionally rather than a flat glorified string substituter (i.e. not actually "just template rendering"), and b) the control and abstractions needed to make good UIs out of nested tables.
Sure, but you're still going to be using "20 MB of inscrutable JavaScript". (Unless you use Wicket, but I'm not sure that's an option for emails, and would likely trigger the same complaints anyway). I mean, I hope you're not using the component style rendering layer for Python that I published ~10 years ago, because I haven't maintained it, and as far as I know there aren't any others.