Is Confluent system design really where people fail?

Just started testing out the waters with Confluent and been going through posts here. The question bank is pretty small and well-documented, coding rounds seem manageable tbh. But I keep seeing people say they passed both coding rounds and still got rejected because of system design.

Is the temporary email system design that hard to nail, or is it more about the tradeoff discussion they expect from you? Anyone who cleared the system design round, what did your approach look like?

YOE: 4, mostly backend infra.