Good points from the OP.
It is however missing one of the largest changes, which it that you get Advantage from High Ground, and Diadvantage from low ground. Advantage/Disadvantage is an effective +/- 4 to dice rolls, which means a +/- 4 to AC.
Remember the Harpy fight, where you're stuck with permanent Low Ground Disadvantage, with difficult terrain and climbing between you and the closest high ground?