How does the Sanskrit used in the Mahabharata compare to that of the Vedas or prashastis?

It is far simpler and probably widely understood.

The version of the Mahabharata we have been examining is in Sanskrit, although there are also versions in other languages. Nevertheless, the Sanskrit used in the Mahabharata is less complex than that found in the Vedas or prashastis, making it likely that it was widely understood by many.

Historians typically categorize the content of the present text into two main categories: narrative sections, which contain stories, and didactic sections, which contain prescriptions about social norms. Although this division is not entirely rigid, as didactic sections may include stories and vice versa, historians generally agree that the Mahabharata was intended to be a dramatic and emotionally moving story. They believe that the didactic portions were likely added at a later stage in the text's development.