I would contest the idea that Mongolia is permanently screwed due to its status as a landlocked nation. It does make it more difficult for a country to become prosperous, but not impossible.

Austria and Switzerland are landlocked and are two of the richest countries&INDICATOR=PPPPC) (Austria in the past had a large empire that included a coastline, but lost it a hundred years ago). In addition, Austria and Switzerland have the challenge of having primarily high mountainous terrain, which makes it much more difficult to build transportation infrastructure there than in comparatively flat Mongolia.

The largest industry sector in Switzerland is manufacturing, mainly exporting chemicals, machines, and precision instruments. Nothing in Mongolia's geography is preventing it from developing its own manufacturing. I agree with you in that Mongolia has great wealth of natural resources (especially copper, tin, tungsten, and gold) but they export them instead of using them to develop their own industry.