Ok, a little foreword first: I picked up backdrop after disappointment with D8, two days ago. I'm in the process of creating very basic theme for my page. I can't quite wrap my head around layouts concept, because to me themes and layouts seem to overlap in function.
Another thing is, that I don't like using available templates, I like coding from scratch. This way (either drupal, wordpress, or else) I have least amount of tags in the code, tidy css, and this workflow is also the fastest (I don't have to wonder what the author of template had in mind making 12 x 9 css grid, etc).
So, I've created really simple custom theme (page.tpl.php) hoping that it won't be neccessary to even touch layout system. Just a few divs, header, footer, menu on left. I was able to get menu to render. But I'm unable to render page content, because $page variable is is one big mashup of tags from start to finish - i. e. whole page source.
It's practically the only thing that keeps me from finishing my work for now. Is there a way to just render page content without the hassle of creating layouts and whatnot?