Anybody can curate. Curating a work doesn't require an exclusive copyright to publish that work. Michelin curates restaurants without charging their guests for admission.

You can even start a subscription newsletter titled "rtpg's best of Arxiv", containing curated links to a shortlist of the highest quality research you can find. It could become very prestigious for researchers to be mentioned in your newsletter, and your own reputation will hinge on the quality of the papers you link to (and the ones you leave out). Even so, this service still doesn't require that you host or own copyright to those works!

Nor does this arrangement require that any one work be found on only one single curator's shortlist and no others.

There are prestigious open-access journals that are curated in exactly the same way Elsevier ones are. Curation is completely orthogonal to whether a paper is owned by the publisher cartels.