In a way it does stifle creativity, since the designer can’t just do whatever they want. However this is necessary. If designers could do whatever they wanted without thinking about the user, it wouldn’t make for a very good user experience. When designing for a client it is important to use their design system properly, since it’s a part of their brand. Designers design for others, not for themselves. Designers can be creative while also following the limitations of design systems and design patterns. They can use these guidelines to guide their creativity.