[nvarsj]

The vast majority of engineering design happens async - by typically a single engineer, puzzling/experimenting over possible solutions and then creating a design doc. Discussion then happens synchronously. Solving a complex design problem on the spot is not the norm.

I personally find system design interviews pretty tough - it's not a mode of operation I ever experience on the job. To solve them at Big Tech, you pretty much have to memorize many design patterns and be able to regurgitate them on the spot. Like algo questions, it's testing your ability to work hard to prepare more than anything else.

Not to say this doesn't have value as a filter, it's just not testing the thing you think it is.