I think it’s the ability to illustrate and edit photos and create ‘creative assets’ that sets designers apart from engineers.
User flows and architecture and ideating on how the product works are shared skills between designers and engineers, but engineers generally can’t draw or create visually impressive assets beyond ‘flat’ design/layouts. Designers can (should) do that work as those are skills unique to them that no one else can bring to the table.
I don’t know that I would hire a designer who couldn’t illustrate or create great graphics, especially with a screen based medium. It doesn’t take a designer to come up with product ideas around user flows, layouts, etc. But only a designer can create stunning graphic images.