Dangerous terrain test only apply to a specific type of hill, the scree slope, in which the ground is assumed to be uneven and difficult to traverse. Given the frequency with which my models fall over on this particular hill, it seemed like an appropriate rule.
I have had a soft spot for 5th edition for a long time, I probably played more games with it than any other edition. But, until Age of Sigmar (which in my view is really a different game) I have always kept my armies up to date with the latest rules and I have a fair few models with no rules in 5th edition.
Plus, I rather like the more uncertain and random nature of 8th edition, it's more interesting when playing against yourself.