The Real Solution
The solution to bad posts that have no value is for them to be deleted after a sufficient time has passed after they're closed. For posts that clearly have no value at all, that can be a very short time.
Duplicates are actually deleted automatically in accordance with the same rules that other posts are deleted automatically: if they're unanswered without positive score, the Commmunity bot will delete them after a while. (Of course, we can and should be willing to delete posts manually when we know they aren't doing anybody any good.) So if we have long term duplicates that you consider low quality, that should be discussed in detail.
It's not good for the site to have valueless posts of any kind. Closing questions with a close reason other than duplicate doesn't address the issue of the site being littered with low quality closed questions. If there is any real issue here, it seems to be it must be that.
This shouldn't be a problem for reviewers unless reviewers are reviewing improperly. (And if so, that is the real problem.)
When a post is in the close queue, the job of the reviewer is not to decide on the narrow question of whether or not previous close reasons were correct. Instead, the reviewer's task is to look at the post and determine--as independently as possible from other voters--whether or not it meets any of the criteria for closure. (Of course there is also, in borderline cases, the task of weighing all the reasons one can think of for closing a post against all those for keeping it open. But usually, we just look and see if the post belongs open on the site.)
If reviewers have to slow down to think more about posts, good. Anything that achieves that is a good thing.
If a post has close votes (or flags) for closure as a duplicate, the reviewer should consider the master question, other questions they're aware of (sometimes searching is necessary), and also all the other close reasons.
If a post clearly fits another close reason, reviewers can vote to close it for that other reason. It's neither necessary nor beneficial for reviewers to deliberately make any effort to vote in accordance with the way others have already voted.
Consider that it is a deliberate design decision to only show reviewers if and how many close votes a post already has, after they have decided they think they want to close it and clicked Close.
Reviewers who prefer to select other close reasons are particularly unburdened by this issue.
Of course, in the case of duplicates, it's often necessary to examine the proposed master question, and for posts that are not properly commented ("possible duplicate ..."), that may involve clicking Close to view them. But if you know a post qualifies for closure based on another close reason, considering whether or not it's really a duplicate as proposed is entirely optional.
I don't agree that it's always better to pick close reasons besides duplicate whenever possible. I'll avoid discussing that particular issue here since I know you're making a new meta question to discuss that. But if that is true, it's especially clear that the reviewer confusion issue is not a real problem: If you strongly prefer to close for reasons other than duplicate, then you'd only be considering closing as a duplicate if you've already decided no other close reason applies. But the posts you're talking about are all posts where some other close reason does apply...
