Camel riders are definitely the right unit choice to deal with Keshiks. They are good against crossbows since you don't take bonus damage from them.

With how long the Abbasid age up is, you can't afford to just sit back and go for your own. The timing, especially with the Kurultai push, would be too strong.

Mangudai can pepper down Horsemen. Since everything Mongols have is a cavalry unit, Abbasid's archers and Spearmen are always playing catch up.

If you have two or three Camel Archers, you can raid trade even better. They have 11 base damage and are a ranged unit. The debuff is fully impactful — the Khan, Mangudai, Keshik will hate this Camel.

Without Iron Undermesh, you actually can't contest Mangudai with Horsemen.