The big problem with implementations in interviews (or coding challenges in general) is that they don't test what the interviewer is thinking they are testing,

The big problem with implementations in interviews (or coding challenges in general) is that they don't test what the interviewer is thinking they are testing, and it is usually a clear indicator that the business looking to hire has some major shortcomings in their developers. For what it's worth I've been on both sides of the table. I don't bother with code when I interview because it's a waste of time. I may show a (non-critical, not-worth-NDAing) section of code to a prospective employee and have a discussion about it, but in general I can suss out whether someone knows what they are doing in less than 30 minutes just by having a conversation with them. Why make the applicant or me wade through 2-3 hours of code and not get a sense of what they are truly capable of when I can talk to them for 30 minutes and assess their technical ability, communications patterns, and fit for work culture simultaneously? The smartest people I've ever worked or interviewed with don't bother with code as interview.