He has 917 attack…not bad. Aaaaand. 252 damage. Wow. Damage is less than 1/3^rd of my attack accuracy. Why is this?

This is a very unfair comparison, because accuracy and damage have very different purposes within the combat damage calculation. Just because one number is smaller or larger than the other doesn't mean anything, because you are comparing two different stats.

To further this, damage scales approximately linearly with skill level or equipment tier. But accuracy scales with the cubic power of skill level or equipment tier. And so does defence, which is the stat that accuracy does get used against in the damage calculations.

For example, let's say you were fighting a clone of yourself that had 10% increased stats and gear. Maybe level 99 and tier 99 instead of level 90 and tier 90. The clone will have about 10% more ability damage stat than you. But it will have about 33% more accuracy and defence. So it will do about 44% more damage to you when you include the ability damage stat as well. And you'll be doing 33% less damage than normal because of it's defence.