To be fair, these interviews provide a lot of valuable signal in terms of how you approach tradeoffs and explore a problem space. In that sense they're quite similar to the work I did at $dayjob, just in a compressed timeframe (which makes it challenging). As you said, the questions are similar to real world systems at these companies -- it's just that you won't have experience with these systems unless you've worked at these companies before. It's a catch-22.