In the specific question, I agree: closing as Too Broad would be better. If the question is edited, the case for reopening should be based on whether or not the author managed to
"add details to narrow the answer set", not on whether it is now sufficiently distinct from another Too Broad question. (I think I voted as too broad, but I may be wrong; in any case, the majority reason is the only one displayed.)
However, there are cases when it is appropriate to close as a duplicate of another closed question.
Double posts by the same author
Often, the closing reason from the first copy can still be used for the second. But what if the author than fixes both versions and they no longer qualify for that reason? Both will be reviewed independently by Reopen reviewers, and probably reopened. Then the answers get split between the copies, until someone recognizes duplication and votes to close again...
Even when the second copy of a double post is not as bad as the first one, it is still a duplicate and should be closed. Users should be editing their on-hold questions, not asking them again. If the moderators were not already overworked, I would suggest a nuclear solution to double posts: one-click deletion of the second copy.
Exact duplicates closed as a abstract duplicate
Someone asks for a solution of $x^5-1=0$. There is already an answered question A about $x^5-1=0$, closed as an abstract duplicate of question B about $x^n-1=0$. In this case, I would vote to close as a duplicate of question A, since it is a closer match. The user is free to follow duplicate banner to question B from there, if the answers to A were not sufficient for any reason.