A lot of backpackers got around featureless rugged terrain for years without GPS and did so without trial and error. But having said that if modern technology is available to make life a bit easier in places like that then I'm not against it. But as you mentioned, you need to know how to use maps and a compass in case GPS or the smartphone technology fails either due to satellite failure, battery failure, unit electronic failure, breakage, whatever, you don't want to be somewhere remote and suddenly find yourself in a serious life threatening jam because your relied on your GPS and was clueless concerning maps.

I ride into remote areas, on road not off, and I go as far as to carry a spare tire in case a tire gets destroyed, a rare event granted, but it can happen and has, without the spare I would have had a couple daunting long walks in very high temperatures, and one person I ran into would have had the same problem had I not happen to come down the same road and gave him my spare tire. So knowing how to use both GPS and maps is wise even though going to the maps due to GPS failure might be a rare event, you don't want to not be prepared for such an event, thinking that may not happen to you could cost you your life and those that are with you. Think smart.