Yeah that really sounds like he's hesitant to give hope and is concerned more about balance issues, but the game already has that handled like I said. If you bring 2 nodes to their last hit like you did when farming favors and had maps show up on 2 nodes, 1 dragonskin and 1 wyvernskin, the 2nd map would still show up in the node if you grabbed the first but the game prevents you from taking it, even though it's not breaking any uniqueness rule.

So tl;dr there's nothing unbalancing about allowing them to stack.