The current phrasing is a bit different from what it was when this question was asked:
This question was marked as an exact duplicate of an existing question.
I think this phrasing is fine, so I'd say this is "status-completed. This may not completely get rid of the cognitive dissonance of an older question closed as duplicate of a newer one but it's certainly better phrasing than it was. It's simpler and doesn't lead to confusion if the question isn't answered (as it can occasionally be closed as a duplicate without the duplicate being answered).
I suppose that, if we want to be even more clear, we could replace "existing" with "another" -
This question was marked as an exact duplicate of another question.
On a side note, I'm glad that the "ask a new question" phrasing has been removed - if we already have one question from them that's a duplicate, we don't need a third that will possibly also be closed as a duplicate... which we will again tell them to ask a new question to clarify their question... it's a never-ending spiral of duplicate questions.
We should be telling them to edit their current question to clarify (preferably before the question is even closed in the first place) - which should make it clear why it's not the same as the existing question and have it reopened. The goal of closure is to edit and reopen - if it can be edited. Or, if it can be caught in time, to edit before it's even closed!
The guidance here on MSE supports the edit to clarify practice:
Someone flagged my question as already answered, but it's not
Instead, go back through your question and reword it a little. Maybe add a sentence or even just a few more adjectives. Also say something like
I have read [title of other question, linked to it] and it's helpful, but doesn't address [whatever].
This should be phrased in a way that makes sense even when the close votes are all gone, and is generally best in the body of the question, not as a comment under it. Not all close voters read the comments.