Ask HN: Do interviews give higher signal than an online tests like HackerRank's?

It seems like most technical interviews involves asking an algorithms/data structures/programming question and watch the candidate solve the problem. If this is the case, why can't we do the same thing via hackerrank or an automated online assessment test?

I can see a few potential reasons

a) A good interviewer can gauge a lot more in an interview and hence that gives more signal. b) Good interviewers can help candidates who are stuck with small hints and that again helps give more signal than someone stuck on an online assessment test

If there is some signal, how much signal is there in an actual interview?