If the question is "marked as duplicate" then there is always a link to the duplicate, where the question is hopefully answered. I think it is a good thing that the same question has answers in a single place. But of course there is a grey zone when it is not exactly the same question.
As for off-topic questions, this is annoying, but I also think it is necessary for any useful site to maintain a focus. For example, StackOverflow does not allow requests for software recommendations even though this a frequent kind of question. But it is not a good fit for the format of the site since you often cannot say a recommendation is the "correct" one.
As for off-topic questions, this is annoying, but I also think it is necessary for any useful site to maintain a focus. For example, StackOverflow does not allow requests for software recommendations even though this a frequent kind of question. But it is not a good fit for the format of the site since you often cannot say a recommendation is the "correct" one.