I switched to Hard difficulty as well and the AI seems more aware now and can see me from further back. I take damage more realistically now too. Man there have been soooo many situations where I've survived with just a tiny sliver of health. So intense. I love how stupid shit like regenerating health are not part of this.
Also anyone who thinks this even remotely similar to Uncharted is a troll or just incredibly fucking restarted. It feels NOTHING like uncharted other than the occasional prompts to helper your companion up a ledge, etc.