UI Design or a Frontend Software Engineer? I'd expect people working on the frontend to just as proficient in time complexity, space complexity, and performance analysis as a backend engineer. I don't particularly gravitate towards companies working in CRUD apps, but single page applications with complex UI flows and data collection can certainly need those abilities. For one, it's not particularly uncommon to have an actual tree in the UI. How would you represent that tree? How are you going to handle it as it grows to thousands of nodes?

I think few frontend developers would consider the work they do to be "UI design".