Some of this has been mentioned so far but from my side I'd say the 5 minute timer yet very complex scenario is something that sets the "candidate" up to fail immediately, certainly if they're typing all this out. You're lulled into trying to cover the big picture but needing sufficient detail (it's not clear how low to go) to make sense. Having a multi-step process where it's progressively more low level as you drill in would be great. When we do interviews we tend to do very high level boxes then drill into increasing detail covering edge cases. This is hard to do in a one shot response.