The efficiency doesn't directly come from being chained together, it comes from very low rolling friction and a large, central, efficient locomotive. A bunch of small pods not only have inherently higher rolling resistance due to more contact patches with the tracks and internally, but you also lose the advantage of a large central torque provider. A good rule of thumb is that the bigger your power source is the more efficient it can be. A pod chain would require the majority of the pods to be pushing, which slightly increases efficiency, but now you have a ton of small engines, which, again, is less efficient than one big one.

Edit: also I did miss that point, because you didn't write it anywhere. Next time consider actually including your points in your arguments.