Closed reports are not lost, they are still searchable/linkable, they are just not in the list of work to do.
This is entirely up to the maintainer, who puts in the work and gives up their time/money to do so. If you want to be in charge on a given repo, put in the work and become a real contributor, if not accept the rules the maintainers choose.
Dupe reports are a signal all by themselves, that's really not harmful, nor does something being closed implied solved.
You shouldn't presume to know what is best for an open source maintainer of any given project - projects vary, reports vary in quality, and the job of maintenance is not an easy one.
This is entirely up to the maintainer, who puts in the work and gives up their time/money to do so. If you want to be in charge on a given repo, put in the work and become a real contributor, if not accept the rules the maintainers choose.