Many of Tamiya's older tanks like the Pz IV D were designed to be motorized and the hull had to be adjusted to fit their standard sized motorized gearbox AND hold a pair of C cell batteries side by side. The sprockets, running gear and tracks had to resemble the real thing but more importantly be able to run under the battery operations.
What is not acceptable is comparing a kit designed when a constant scale was not very important to a modern kit produced during an age when modeler's standards are much higher than they were 40 years ago.
That's like trying to compare safety standards or gas efficiency of a 1970 era sedan with its 2010 counterpart.
Tamiya's original plastic models were more or less motorized toys that you assembled yourself. Fragile detail was designed oversized and sturdier or molded onto the hull so it wouldn't break off when you removed the top of the hull to replace the batteries or fall off when the vehicle ran into a chair leg or living room wall.
Today's kits are more refined with parts designed in scale. They would not handle being motorized.