Just a quick FYI...
You can 100% still get this achievement by selecting 'Rite of Passage' difficulty (which sets Combat, Exploration and Puzzle difficulty to 'Normal') and then lowering ONE of these three difficulties to 'Easy'.
If you lower just one, you will see that the overall difficulty remains at 'Rite of Passage'. If you lower more than one, the the overall difficulty lowers to 'Smart and Resourceful' and will obviously void this achievement.