Is it wrong to say that the past simple is used for very short actions and long actions (the dinosaur example) but for shorter ongoing actions native speakers use the past progressive not the past simple?
According to some books the length of time a situation lasts has nothing to do with the tense/aspect chosen, but in their explanations grammarians use "a situation that lasted a long time" or "shorter ongoing actions" when they explain why a certain tense is preferred in a particular example. So they are still talking about the length of time. These are the examples according to which the past simple seems to be used for very short actions and long actions (the dinosaur example) but for shorter ongoing actions native speakers use the past progressive not the past simple.
The king ruled for 40 years.
By the middle of the nineteen sixties many parts of Europe were experiencing a tremendous economic boom.
Intervention was urgently required-the starving children were growing weaker day by day and there was little sign of an end to the drought.
Many of the survivors were working in the field when the earthquake struck.
Dinosaurs roamed the earth for over 150 million years.
The book fell from the shelf.
The time dinosaurs roamed the earth and the time the king ruled his country is definitely longer than the time people were experiencing an economic boom and the time people were working in the field and the time the children were starving.