I liked GP very much. I found it hilariously funny and not at all one dimensional.
I think Terry wanted to make several points:
a) If you're not careful in the business world, you end up with having sold your business before you even noticed it (bright people with not so much grasp of financial matters falling for Gilt, ending up without the trunk)
b) Free market is an illusion once a quasi monopole (in this case the grand trunk) has been established, since there is enough money there to buy up any competitor before they can become a real competitor and because you can also covertly do things to get rid of competition in other ways.
c) Terry criticizes unsustainable capitalism aimed at short term profit: Since it has been taken over, the Grand Trunk has become less reliable and there's actually no maintenance happening, but patching if something breaks due to lack of maintenance. Because of b) the Trunk doesn't have to fear losing customers, because they've become so dependent on a fast flux of information. This leads to the Trunk demanding high fees for little service and and not caring if the network fails from time to time. In the end the Grand Trunk Company isn't planning on keeping the trunk forever, but to make as much money on it as possible, run it down, sell it to someone else when it becomes unprofitable and perhaps buy it back when it seems it will become profitable again.
d) Certain vital parts of infrastructure shouldn't be privatized because of b) and c), even if they seem to be unprofitable: There's a great quote in GP that is, in my opinion, spot on. I'm quoting from memory, so it might not be verbatim: "Perhaps something like the post office couldn't be run at a profit. Perhaps the profit turned up distributed over the whole populace." Now, a state owned company can afford to run at a loss, because it is financed by the state, which in turn earns more when the people are wealthier. A corporation, however, can not run at a loss for a longer time because shareholders would soon sell all their stocks bankrupting the corporation. That is why, for example, in Germany energy companies sued the state when our politicians decided that all nuclear power plants have to be shut down until 2025 (or sometime near that) - these nuclear power plants are money printing machines and shutting them down costs the companies a lot of money. So the CEO has to do all he can to avoid these losses lest he be held responsible for the losses.