Additional question, should the font weight 600 applies to the whole UI (including panels heading), or just to the page content.
Option 1.1: just the content page (#mainContentArea)

- The admin section is impacted
Option 1.2: the content page excluding the heading title (#xwikicontent)

- The admin section stays with the same weight.
Option 2: the whole page

I’m +1 for option 1.2, as I think the pages content is the place where having weight is important.
For instance, the administration headings (as well as the panel ones) are styled differently.