Seleucid Empire has impressive troop types indeed, but they go down against Egypt in the first decade or so .

Furthermore, i'd classify as overpowered those factions that get an early advantage, so they can get a lot of towns easily as soon as the games starts. For example, roman strength lies more in Hastatii than in Urbans.

Likewise, Seleucids can built Legionary cohorts, but so late in the game i guess it doesn't have much effect anyway.