Part of the problem with the argument about subsidizing rural life helps relieve pressure on the urban and suburban areas is that the numbers do not bear that out. It certainly hasn't significantly slowed the move of the population in the US from rural to urban areas. The general flow of population continues unabated towards urban and suburban areas. Partly this may be because of the inherent efficieciencies, energy and otherwise of such conglomerations over a population spread out far and wide requiring long low volume and inefficient transportation links. This work as long as energy and transportation costs remain low. But once that goes away the move towards higher density population centers is inevitable. And then the primary question becomes what is the most efficient way of providing transportation within those conurberations and between them. In the long run the smaller towns and rural areas will see inevitable decline.
Actually third world countries have more spread out population than say a country like France. Countries like India are way more rural than even the US already. See
this spreadsheet for some real data and projections. This is most likely because subsistence livlihood is still an acceptable mode of life in those countries. It is not in the US and Europe, and there are progressively fewer high quality jobs available in the rural hinterland. The new generation is in general moving out to urban areas creating a renaissance of the urban core in many cities in the US. Unfortunately the planners in the US and specially Congress has romantic glasses on. They will wake up from their fantasy one of these days hopefully, before it is too late. But this is getting far afield.
Within this context, I believe that LD trains serve a purpose of connecting a large number of rural areas along a relatively high density communication corridor between urban conurberations most efficiently, more efficiently than road or air. There are other off the beaten path rural areas that require less efficient means of connection. For connecting large conurberations that are far removed from each other possibly some mix of rail and air makes the most sense. But a country with a well developed highway system is possibly at a economic disadvantage in its ability to develop a rational transportation policy matching the demographic trend most efficiently. However, the net adverse effect of such will possibly become visible way after my generation is gone.