These faces are forming visual interface, e.g. hunks in Magit are rectangular
regions with background color for entire width of the window that can be folded.
Code blocks in org mode are, ahem, blocks. Now those blocks doesn't have
anything like block visually.

> So you are saying that you don't like the new appearance?  The Subject
> says "broke visuals", which sounds like a much more serious problem.

Well, "broke" may be wrong term, here, but lot of themes and packages crafted
in a way to display things like that, and now all of those things displayed accordingly
to a new setting, which in turn means that:

a) package maintainers should update *all* their packages to look like before the change, and
b) maybe Emacs could treat `nil` here as "do not affect", and specify symbols to set this to different
   settings, like `:extend t` or `:extend 'EOL`, and `:extend 'noextend` to disable. Though, I do not
   know how code was changed, so maybe there's no way to treat `nil` as "do not affect".