Uhh, the Macedonians were not Persians, nor was Phillip Xerxes.
The difference is that when the Greeks fought the Persians the Greeks had a vastly superior tactical weapons system, though at first, such as at Marathon, they weren't really aware of it. Something like WWII tanks vs. WWI or WBTS infantry.
By the time Phillip came around he had improved significantly on the Greek phalanx, while they hadn't changed much. It was now sort of like Gulf War tanks vs. WWII tanks.
While there's little doubt Athens and the other city-states, especially Sparta, had degenerated, that isn't why they lost. They lost because their part-time citizen-soldier militia couldn't stand against the far superior professional armies of Phillip and Alexander.
I think Philip I of Macedon did a pretty good job of dividing the city-states prior to military operations while Xerxes did a pretty good job of uniting them.
Agree with your other observations, btw!