I do think that design systems can be helpful for smaller, or even 1 person teams as well. It helps you to apply meaningful constrains for your design and reuse common components across the product to shorten development times.
With the library we have both designers and developers can construct completely new views or modifications fairly fast. https://twitter.com/karrisaarinen/status/849733176150773761
Where the React-Sketchapp comes in is help us to keep the system up to date for designers, and in the future build other tools that can help the design workflow.