Ooh I hope that's the case because that would be much more convenient

Edit for anyone who stumbles on this: it works exactly like the above commenter described! It looks like there's some opportunity to better communicate what DLC the "copy" you select is installing since it doesn't show a full list of DLC but it at least shows who's library it's pulling from so you should be able to infer the full DLC list based on who has all of the DLC