Having a designer in your team is key for building good products, but not for the reasons you think. While hiring designers, most people primarily look for visual skills which are only a small part of what makes a designer essential. In addition, designers have other skills (I like to call them superpowers) which can be critical in any team.
Keen observation and empathy
This is what allows designers to understand the problem a product needs to solve. They don’t shy away from talking to users as well as finding other ways to get the insights they need to design a solution that works. Good designers can turn the most mundane feedback into actionable insights. This is not to say that they spend countless hours and money on gathering feedback. I’ve seen designers who are able to turn a bus commute into a user research session. Their ability to get into other people’s shoes enables them to deliver products that users love.
Creativity is not only about coming up with great ideas, but more about identifying the simplest solutions that can solve the problem at hand. Good designers can tackle complex problems and come up with novel solutions. But they also know when to not reinvent the wheel. Their strength comes from knowing when to follow the commonly established patterns and when to break the mold.
Good designers are a master of their craft. They are able to create prototypes to quickly validate ideas with users. They know prototypes will help developers understand and architect the product before writing a single line of code. They create prototypes to get everyone on their team on the same page. They know that they are not creating art, but a vision of their product to help their team move fast.
Although these superpowers are typically expected in designers, I think that it is possible for other people to pick them up as well.