I think the counterpoint to this would be Google Search. The core product is incredibly simple from a frontend perspective, but the backend is world-class engin

I think the counterpoint to this would be Google Search. The core product is incredibly simple from a frontend perspective, but the backend is world-class engineering. I think making information usable is hard. This means that the burden of the development falls on whatever is making the information useful. If you simply can query an API and get stuff back that's valuable because the data is already processed, UI is pretty easy (aka Google). If your backend is returning raw data that needs to be organized and displayed, and users need to be guided through complex processes that are just simple CRUD operations server side, you have a much harder UX/UI challenge. Most things fall somewhere in the middle.