Historians and specialists in ancient Iranian religion generally treat Vishtaspa as a figure whose historical reality cannot be confirmed through evidence independent of the Zoroastrian tradition itself, and whose specific identity, if he existed as a genuine historical ruler, cannot be securely matched to any other known figure from the period. The name recurs in later Persian tradition, including as the name of the father of Darius the Great, the Achaemenid emperor, which has occasionally led to speculative attempts to connect the two, though most specialists regard this as an identification the evidence cannot support given the very different, and disputed, dating usually proposed for Zarathustra's own life.
The most vivid details of the conversion story, including the healing of the paralyzed horse, are widely read by scholars as later legendary elaboration added to a much sparer original narrative, following a broader pattern in which the founding accounts of ancient religious traditions accumulate miraculous and dramatic detail over generations of retelling before being fixed in the written sources that survive today.
What can be said with more confidence is that the Vishtaspa narrative reflects an authentic and early Zoroastrian conviction that royal or aristocratic patronage was necessary and providential for the faith's establishment, a conviction that continued to shape the tradition's relationship with royal power throughout the long history of pre-Islamic Iran, culminating in Zoroastrianism's eventual status as the state religion of the Sasanian empire more than a thousand years later.