That's the thing with small factions vs. the Arche - don't be afraid to take them on and steal their cities - it weakens them. They are a monster that will keep returning for more, but take their cities, pump out troops, and eventually you will secure yourself with them. Tactical skill also helps. I learned this by playing Hayasadan and Saka Rauka, haven't played Pontos since I was a noob. Check my Saka AAR for an experience with the AS - THEY JUST DON'T GIVE UP!!!