Compare this for example to the NFL combine. Or the amount of time and money put into farm systems, feeder teams, and scouting reports. Why not pay the candidates to solve an engineering problem and judge the output? I don't have the answer, but I'm fairly certain that there has to be a better way than stress traps and good-ole-boy networks.
I work very hard to tailor my interview questions to the actual background of each particular applicant so that they can in efffect ask their own questions and demonstrate ability (ala "oh that's interesting how did you solve that problem, and what if you did this instead how would that work in the design, here's a whiteboard show me, etc). It is very hard and I regret very much the "good hires" I have probably let go because they couldn't engage well with me or talk about their own experience well. This obviously takes time and effort so I depend on recruitment/referrals properly to weed out wastes of time.
Is anybody working on this problem? It seems clear google isn't and HR innovation is extremely profitable.