I was busy and lost track of this.
Perhaps I'm blurring the two. It was certainly the case in the democratic period, running right up to the rise of Makedon, that there was a suspicion of aristocrats choosing to fight on horseback.
There's no maybe about it, the notion that stirrups are required for a couched charge is nonsense. Alexander's Companions were charging-home, heavy cavalry, none of them had stirrups. Their primary purpose was to give horse-archers a good seat.
There isn't really a lot of time between the re-establishment of democracy in 510BC and the Ionian Revolt in 499BC, so I think the point is rather moot.
I'm pretty clear on the differences between Greco-Persian Wars and Hellenistic era. I was already distinguishing in that part you quoted between the Greco-Persian Wars, the wars of the Delian League and those of the Peloponnesian War. The Hellenistic era is often ignored altogether, except as the prelude to the era of Roman dominance.
For the most part, Greece itself didn't have professional armies in the Hellenistic era, it still relied on citizen-militias. They changed back and forth between hoplite/pike/thureophoros models as they won and lost in conflicts. The closest anyone came to professionalism was if they turned mercenary.
Even Alexander didn't have a lot of use for Greeks on his campaigns; the fighting was done by Makedonians and various allied nations, Greeks might be put on a flank or more often used as garrisons to hold strong points while the rest of the army moved on.
The professionals in the Hellenistic were Makedonian settlers and other Hellenes and Hellenising peoples given grants of land in return for service. And mercenaries.
No they weren't different, that's a modern division that doesn't apply. Athletes trained for the Olympics and other major games, which contained a host of martial events in them; running in and out of armour, throwing javelins and discus, boxing/wrestling (pankration), fighting in armour, horse-racing. All those events were practise for war. We have the example of the athlete Dioxippus famously beating one of Alexander's soldiers in a set-piece bout.
Maybe, but the minimum requirement for a hoplite wasn't a full panoply, but a shield, helmet and spear. That isn't as high a bar as also having cuirass/thorax, greaves, possibly arm and thigh plates.
I was thinking of countless Athenian and other Greek generals, from Miltiades down, who all fought on foot (often in the centre of the front rank) even though they were of the highest social classes and could ride.
Add to that the low proportion of cavalry in the battles of the Peloponnesian War compared to those of Philip/Alexander. There's no way the aristocracy were only represented in the tithe of cavalry present.
I don't believe anyone would have cleaved strictly to the Solonian divisions, there would be aristocrats too impoverised to fight in the saddle and richer artisans who nevertheless continued in the traditions of their fathers and fought in the phalanx.