One of the challenges with CSS is that it has evolved tremendously over time. Over that time technologies like CSS preprocessors were invented to try and deal with the shortcomings of CSS at the time.
This is rather analogous to jQuery and IE6. My gut feeling is that in 2021 if you are a designer who is seeking to find simplicity with web standards, and not needing to support legacy browsers that one is best off avoiding CSS preprocessors and instead spend more time learning how to leverage the full power of modern CSS.