Heroic sacrifice is a very common trope in propaganda.....Also, I wouldn't claim him to be the overall hero of the battle of marathon. That would prob be Miltiades, Themistocles, or Aristides.

The popularization of the tale of someone running matarathon wasn't popularized until Plutarch wrote about it nearly 500 years later and he named the runner "Eucles, although also possible Thersippus of Eroeada", then around 100 years later Lucian of Samosata gave the same story but names the runner Philippides (not Pheidippides).

Philip the demigod was so tuff he could run for two days straight and not break a sweat.

And there is a difference between mythology and history.

The first-known written account of a run from Marathon to Athens occurs in the works of the Greek writer Plutarch (46–120 AD), in his essay "On the Glory of Athens". Plutarch attributes the run to a herald called either Thersippus or Eukles. Lucian, a century later, credits one "Philippides". It seems likely that in the 500 years between Herodotus's time and Plutarch's, the story of Pheidippides had become muddled with that of the Battle of Marathon (in particular with the story of the Athenian forces making the march from Marathon to Athens in order to intercept the Persian ships headed there), and some fanciful writer had invented the story of the run from Marathon to Athens. Magill and Moose (2003) suggest that the story of the Marathon–Athens run and Pheidippides's death is likely a "romantic invention". They point out that Lucian is the only classical source with all the elements of the story known in modern culture as the "Marathon story of Pheidippides": a messenger running from the fields of Marathon to announce victory, then dying on completion of his mission

Maybe he had a horse?