Design is a process that is not exclusive to “designers”. Everything that is made had to be designed, consciously or not. However there’s a considerable bias towards design as a visual craft, and focus on associated tools and techniques. That is what you learn when you are starting out in design. But the more you practice it the more you start to see design as something much more abstract and powerful.
Business is similar. If you start out in business as an individual contributor, you learn the knowledge of finance, accounting, marketing, etc. These are all bundles of technical skills. But as you grow with your business you start to see it as a system of systems. You start to develop a more holistic view of what it takes to manage a complex economic, technical and social system.
I think that as we grow in experience the kind of knowledge that we need to acquire changes. I think that we need more and more people who are able to connect dots between domains. We have a culture of creating specialists, and we sometimes lack the ability to look laterally and use language that crosses domains.
In this spirit, learning from other disciplines than your own, is always a good idea. Doesn’t matter if you’re a designer, an engineer, or an MBA. (By the way I have education and work experience in all three).