What the author omits [or doesn’t know] is troubling. Two quick examples: Carthage. He totally ignores it. Then there’s the Magyars. They don’t arrive in the Hungarian plain until much later, like 300-400 years after the Huns do -and the Huns didn’t arrive until the late 4th-early 5th century, AD. Indeed, except for the Scythians [who the Persians had been fighting since the time of Cyrus the Great [they killed him]in the southern Steppe, there weren’t a lot of people around up that way [the great migrations started later] for the Persians to fight. And not much [wealth, ports, etc] to fight over.
Still, going with the author, I propose a slightly different result. With Persia beating the Greeks, the Greek colonies in Sicily and along the Mediterranean littoral will seek alliance with Rome. Rome will occupy Sicily without the need for war with Carthage. The two may ally against Persia. Roman military reform [weapons, organization, tactics] brought about by conflict with the Gauls in the Po valley would accelerate.
If there was a confrontation,a Roman- Cathaginian Army: Roman Infantry, Libyan infantry and Numidian cavalry would clean the Persians’ clocks. And unlike Alexander, the Romans would have destroyed Persia in it’s turn [see Third Punic War].
One other note. Xerxes regretted burning down Athens as soon as he did it [as a reprisal for the Athenians torching a Persian provincial capital-kind of like the Brits and DC in the War of 1812]. He ordered it rebuilt the next day. He sought Greece’s submision, and incorporation, not its destruction.
I disagree with that -- the Persians had to initially fight off the Babylonians and the Medes and prior to that the all-powerful neo-Assyrian Empire had been defeated.
Beside the Scyths, the Persians had to contend with powerful Indian dynasties and the Egyptians
and wealth -- there was a lot of it in the fertile crescent, indus valley and Canaan.
Good point - mercy and the SPQR were opposites