The Flow of trigger resolution is right here:
As point number 2 states, this all can be trigger in any order. These are all the triggers separately:
After a [character] attacks an enemy/minion---------------> This is the same as using a basic power, in this case exhauste and target an enemy
After a [character] attacks and damages an enemy/minion
After a [character] attacks and defeats an enemy/minion
After a [character] is attacked
In your code,
AfterUnitAttackUnit = AfterUnitUseBasicPower
The last source to settle is a direct quote from FFG, I'll try to get a response on the matter