I generally agree with your advice, but what I've seen at a lot of companies is that HR will put in policies that really tie managers hands. I know one place I worked at was notorious for underpaying people, and HR was stingy about how large of a raise someone could get, but if you brought in an offer letter they'd almost always match it. Which IMO is a very dumb policy -- basically the only people that got paid well were the people that already had one foot out the door.