Ah, then I'm not the only one who noticed that.
I accept that XCOM and DOS2 didn't take z movement into account either. But that sometimes resulted in hilarious ways of movement - you did not run around a building (20 meters) but instead climbed 10 meters upwards, another 10 meters upwards, walked 5 meters across the roof of a building, and then climbed 20 meters downwards - all the while loosing less movement ^^
But I guess finishing the game is more important than addressing such minor nitpicks.