Rome has a unified (i.e. standard) military. All legions are organised more or less identically.

The Greeks do not have a unified military. They are an alliance of individual city-states.

So, with the Greeks of Koinon Hellenon, what you really have is a Spartan army, an Athenian army, and a Rhodian army. All organised slightly differently, even if they use very similar units. Sparta might emphasise a head-on clash with old-style hoplites and missile troops in support. Athens might emphasise battles of maneuver, outflanking peltasts and skirmisher cavalry with new style hoplites and phalanxes in support. Rhodes might emphasise missile fire with Rhodian slingers, with classical or levy hoplites in support. Each army will have its own preferred fighting style, but be able to combine with the others if necessary when a very large field army is required.

Later, after expansion, Koinon Hellenon might have a Corinthian army, a Thermon army, a Syracusan army, a Cretan army, a Massilian army, etc, etc, etc. All organised slightly differently, with the tactical emphasis on what locally-produced unit is the most effective, and its own style.

Romans = uniformity. Greeks = variety!
and:
Romans = simplicity. Greeks = complexity!

Basically, no two Greek armies would be exactly the same. Unlike Roman armies.