We might have pushed the limits with coding questions. Why do you need 5 coding rounds? does one programming problem not clarify if this person can code or not?
The coding questions are not literally "Can they physically write code or not?" They're evaluating your problem solving skills and coding skills.
There is some inconsistency though with someone's performance in coding questions. Someone usually won't bomb one and then do great in another (although they might feel as though they did). But someone might do mediocre and then do pretty well on the others. Asking multiple questions is just getting multiple data points.
I understand Big4 doing this as they're bombarded by resumés, but the problem starts when mom'n Pop CRuD shops start aping these blindly.
The point of these questions is basically to assess intelligence (as it relates to coding). It's not about having you solve a specific problem because you might need to solve that exact thing in the real world.
You're right though that part of the issue is a bunch of companies trying to replicate the Google process (which might not even be right for their company) -- and then not knowing what it's all about. So they ask super common or really easy problem, which don't even test problem solving skills.
Based on my own personal experience, this is my assessment of the interns who knew too much about interviewing questions
They performed very badly compared to someone who did not pay enough attention to interviewing questions. Its as if the more they read about the various interview questions online, the less confident they were because there is always a tricky "problem solving question" they cannot answer.
They showed reluctance to explore any new areas of engineering except writing java code. practically no curiosity in anything else. They truly believe that their job will be only writing more java code.
Next time if you interview, change the context of the interview and talk to a new grad, some of them had solutions to 500 common interview problems and read every cracking interview book and blog and it still did not get them a job.
There are absolutely people who "learn" dozens or hundreds of problems and then still don't get a job. That's actually a good signal about the interview process. Preparation shouldn't land a bad engineer any ol' job they want.
Unfortunately, it sometimes does -- and that can happen when a company asks easy or well known problems. Far too many companies do that.