I do believe this is probably useful for people interviewing, but on the other hand it reads like mostly complete bullshit and largely social signalling rather

I do believe this is probably useful for people interviewing, but on the other hand it reads like mostly complete bullshit and largely social signalling rather than measuring any sort of skills. The fact that you can be coached to pass these interviews with zero practical experience designing systems (Even toy ones or hobby projects) shows that there is very little technical skill involved. Someone who has designed a real production system is still likely to fail these interviews unless they understand the social nuances that interviewers are looking for in a system design round.