Yeah from a debugging point of view, there isn’t much difference between dev/prod for CSS files.
But going back to the ‘live reload’ problem - that is CSS-specific. If stylesheets from a newer version of Discourse are inserted into a page running an older version of Discourse, that is likely to cause surprising issues for end-users.
That’s why we updated things so that the CSS update is deferred until the next page navigation, so it now lines up with the JS updates.