Yes that is so very true, and is really why the Timeline is such a neat and unique (and, as you said essential) component of Discourse as a robust forum platform.
But, for example, if (by design) a site mainly serves articles or blog posts, those types of sites (often by small or self-publishers) aren’t expecting lots of replies and conversations (and may not want to manage and moderate conversations ongoing). Those articles or blog posts are often timely and meant to have a short shelf life.
Discourse can easily be a superior platform even for those more simple sites like blogs and publications. For all of the reasons we know and love Discourse with it’s robust feature sets which can be initially turned off while not needed, but are always ready to be turned on when needed, without creating a Frankenstein monster site with a bunch of third-party plugins, hacks and add-ons.
I use my nOObish.me Discourse site as one of my blogs. I have posting replies/comments disabled. As a result, I don’t need the Timeline, and I can easily hide it with just a tiny bit of CSS.
When I use a Table of Contents on a Topic/Blog Post it uses that otherwise empty block of white space on the right side of my Post. But if I don’t use a TOC I think that empty white space seems odd. I think I should be able to selectively remove it in the Composer (to reclaim that empty space to widen the content of my Topic post) and I can do that selectively, per Topic, using this method.