One big problem as a Stack Overflow viewer who comes from Google is that many times the top result for a search leads to a question/answer that is a dead end. The question is valid but it is closed because it was asked on the wrong website (Stack Overflow vs. Stack Exchange), it's too subjective, it's a duplicate, etc. Or the question is downvoted and there are no useful answers.

Another issue which comes about from the overzealous duplicate tagging is that not all software engineering questions last forever. If someone is asking how something works in C89 and gets the best answer, and then someone else asks the same question five years later, the answer will be the same. But if it is a question about JavaScript or new C++ or Python, then answers can get stale pretty fast. One workaround the community uses is taking those questions that are top hits or top quality and keeps editing them year after year. But that only works for the high profile questions and answers. The policy hurts the site overall.