RTF is a global modification that replaces all towns in the game.

The Greeks could simply have a different armor style. In Skyrim, the Imperials only have the equipment and titles of the Roman Legion – that’s enough.

The Dark Elves have minotaurs and hydras; you could make elf-hoplites, and that’s it.
It’s easier to create Romans because you can use gladiator armor for non-standard units to maintain visual consistency.

For the Greeks, you can have archers and mages in tunics, and infantry in hoplite armor – I think this is the minimum number of units needed (like the Sylvan faction). The rest can be monsters, but I won’t do that – I can’t make tunics, and there are no units in tunics anymore.