IMVHO any of those kind of infra is a big waste of resources. The cost of certain infrastructure is simply too high.

Now we probably all know the classic economic theory of density, that state cities are needed because people together innovate more, create economy of scale etc, unfortunately too many forget the second part of such theory: a certain amount of density is needed, being more dense just skyrocket costs and create so many issue to nullify any eventually remaining benefit.

High speed trains, and in general ANY big infrastructure fall in this very case, because density does not mean just big cities but also infrastructures to serve them. A big railroad, commercials one included like the Chinese project across central Asia to Europe, means serve a high density area from production of another density area. Too dense in both case to give benefits stronger than their downsides.

IMVHO while for a very big timeslice of human history classic cities was the best density on average, now the best density is a sparse Riviera where resident and production are intermixed and near enough, with just few punctual dense complex for certain production and services like big complex for automotive/aerospace/naval/defense, hospitals, campus, ... but the rest sparse enough to have anything reasonably near (lower transportation costs) but with room to evolve at a slow and continuous peace. Sure, we are many in the world and some countries simply do not have even enough land to afford such model, but we see how big cities fails and we see how dense area fails equally... It's about time to realize that a certain kind of economic development is not viable anymore and we need another one, with some aspects already known from the past and some others brand new.

Just take metro trains: they are the key to city mobility, the sole that work efficiently at a city scale. Super expensive and move gazillion of people per day... Well, most of them are from the tertiary sector, witch means that most of them can WFH without need such super-expensive transportation means, many others are workers affluent of the tertiary sectors so people who need another job if WFH spread. Only a small cohort remain benefiting from metro trains and for them due to the size there is no reason to have nor cities nor metro.

Change is always difficult and always makes errors and horrors. USA have tried to push car sails the suburb model and was a failure, but not because of the suburb, just because suburb are just residential and workspace are far away. Intermixing them and pushing WFH solve suburb issue, in theory. It does not in practice because suburb themselves are dense enough to have tough time reshuffling from purely residential to commercial and residential mixed. And that's why we need less dense design: because such design might or might not work today and might or might not change tomorrow, if there is enough physical space evolution is possible, if not costs skyrocket not much differently than actual cities or suburbs. Things change, being able to adapt is the key, and it's not a new buzzword like "resilience" is the classic Charles Darwin theory of Evolution: not the strongest, not the today's better but the more able to adapt will survive.