Train can't replace Cargo Freight with rail link. You are talking about 600 container per train vs over 20,000 container per ship, and you can run 2 ships (or more) side by side at sea but there can only be 1 train on a track. If China had to resort to using inland trade road, that's actually a serious inhabit factors. You are talking about 2 to 5% efficiency here.China is well aware of the Malacca choke point, which USA used effectively against
Japan during WWIl.
China has multiple rail links connections for her energies, foods, raw minerals flow unhindered.
China also has land corridors in Pakistan and Burma, connecting ports, away from the Malacca choke point.
There is this possibility of the Arctic sea route as well, the danger of this route is the Alaska choke point but with Russia so close to it making it very hard for any blockage by the USA there.
All of those alternative routes give USA war planners a headache.
In addition, PLA has a strong water navy to ensure the "freedom of navigation" for her trades,
Also, Alaska/Artic route can only run during the summer months and is also choked in Sea of Japan. Which is what the first island chain entailed. That's also why China is so desperately trying to break the first island chain. They currently don't have enough ship that can operate that far into the Pacific. Unless either Philippine, Taiwan, South Korea or Japan let them thru.