What if Xerxes had won at Thermopylae, Plataea and Salamis.....would things really be all that different?

It is quite possible that if Xerxes had subdued Greece and placed a Satrap in governorship...presuming that was his intention, that the Hellenes would have united, and bitten the Archaemenid empire on the proverbial backside. Possibly setting an earlier date for the victories that came with Alexander.
Throughout his life Isocrates called for Hellenic unification to avenge the crimes against the greeks and their gods carried out by Xerxes's army. His call was only answered in his late eighties or nineties, by Philip of Macedon and his son Alexander.
Greek hopolites were superior to the armies of the Great King, Xenophon's Anabasis shows what a valuable asset his troops were to the King.
If the outrages had occurred throughout Greece, particularly down into the Peloponnese, Isocrates might not have had to wait so long.
Ideas that we'd all be speaking arabic or muslims, or that 'the white race would not have achieved dominance' are nonsense.