Speaking only of that which I learned from the video I linked, my understanding is that cold-hammered copper actually hardens a fair amount. There's a demo using an axe with a cold hammered replica copper blade where he cuts down a tree, for example, and some tests using copper tipped spears. Also, cold hammered copper fishing hooks, which had advantages over bone fishing hooks inreparability and flexibility and would have been useful for fishing in the Great Lakes area. There are still tradeoffs, though, and stone tools were still in widespread use for things they were better for, but there was still a lot of utility in cold hammered copper.