Well, in the land of the blind...
Until after the Peloponnesian war, the Spartans were the only-city state with a full-time army. With the exception of some elite forces (the Theban Sacred Band is the best known, but there were others) all other hoplites were part-time warriors. The reason the Spartans could do this is because their citizens did not have to farm or attend to business. They had helots to do that for them.
However, because of constant warfare and increasingly sophisticated government, other Greek city states began to acquire experienced, full-time warriors as well. And from that point onwards, the Spartans suddenly look a lot less invisible. After the defeats at Leuctra and Mantinea, the Messenian helots were freed, and the Spartans could no longer their full-time army or their agoge.
Also, they were never quite invisible to start with: the battle of the champions shows that 300 picked Argives were quite a match for an equal number of picked Spartans. In other words: the cream of the Spartan hoplite-force wasn't any stronger than that of other powerful city states: Sparta's superiority lay in their rank-and-file, not the top-end. Off course, by the time EB starts, Sparta is still a powerful city-state with a proud culture, but they no longer had the monopoly on (or even a large number of) full-time hoplite-soldiers.
In EB, the Spartan hoplite simply represent the regional equivalent of the Epilektoi: a city's brightest and best, equipped with the finest arms and armour that money can buy. The only difference is their culture (morale bonus) and the fact that Spartans were an old-fashioned Pylos helmet. Hence the -1 armour.
I agree there is, at the moment, no point in preferring Spartans over ordinary Epilektoi; but the reasoning for not making them supermen is sound.
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