That is true, but I think it's just that the icons cause you to sort of rely on them and don't really promote actively looking around with your naked eyes. You can just point yourself at the markers while running and jumping and you'll get through most things, mountains included.
No, you won't. You still have to find a way around mountains, and simply glitch jumping up them doesn't work most of the time, especially if you're, you know, actually ROLEPLAYING and not glitch-playing.
Plus, I get so immersed in the world that I am constantly getting lost, map markers be damned, because the world is so rich and detailed that I am paying attention to it, not my map markers.
If you're playing the game through your compass and map markers, that's your own fault.