Make loyalty and also authority a huge factor if you want to represent this. Traits like venal in EBI do little harm unless it will develop in law and trade penalties.

High Authority to could define a strong dynastic king (like Antiochos III Megas). Low could be put on weak kings.

Also the option of rising factions is there now (So Seleucid pretenders like Alexander I Balas can be represented). Has less to do with this, but rising factions can also better represent the Yuezhi hordes.

~Fluvius