Macedonian is able to keep you in feudal. Eventually your Varangian Guards reach six melee armor or ranged armor, and with the Hippodrome Champion and Runestones they get over 1.6 tiles per second movement speed, running as fast as a knight. Your infantry gets absolutely blitzed.

As soon as the second melee infantry armor upgrade comes in, Varangian Guards have 10% bonus health, six melee armor, four ranged armor.

The only real option as Abbasid is to make camel archers against them, but once the Hippodrome Champion comes in, Varangian Guards with a charge can catch up to the camel archers and take them down.

Once the last armor upgrade for Varangian Guards is in, it's just over.

Berserking means Varangian Guards take a lot of damage, so don't walk in while Berserking is active.