I can see where you're coming from. It's frustrating how choosing one path over the other doesn't seem to have any real consequences in the long run. Whether you go through the Underdark or the Mountain Pass, it all leads to a similar outcome with no significant differences.
They should definitely amp up the challenge in the Mountain Pass right from the start. And the idea of using the Underdark to avoid the shadow curse? It's misleading; you end up in the middle of the curse regardless of your choice. I'm not saying they should lock off the Mountain Pass, but they should make our choice about which way to go in the Shadow-Cursed Land matter more and have a real impact, or at least ensure that Halsin's advice aligns with the actual situation.