The goal for OJ is create reusable UI building blocks. So I agree completely that keeping sites simple and declarative is the way forward. I would argue though that if the abstraction well reasoned it doesn't matter if it is in HTML or in JS. It still simplifies things for the programmer and maintainer.

Or another way to say it -- Imagine you can insert a YouTubeVideo as simply as you can insert a div. If that YouTubeVideo component is well tested, then you are actually saving your self time and will make a more robust site.