Agree, it's the simplest way to get a first glimpse of CSS separation. Other than that, such code shouldn't go in production.
Loading the CSS files async. will work too, but keeping track of all style files can become tedious as the project grows (css loaders will not work with @import inside CSS files).
I'm leaning towards the second part of your answer - SASS and LESS separated code is way more scalable and maintainable. Also, learning them shouldn't be such a difficult task. :)