Desperation + Brash Assault confusion

The combo is simple, brash assault secures you will attack twice regardless of the speed of the units, and desperation simply does what desp. does

Brash assault gives them the ability to perform a follow up attack if they are at or below the hp threshold, but it's still performed in the normal attack pattern of your attack > enemy attack > your follow up attack. Desperation makes it so your follow up attack is performed immediately, like this: your attack > your follow up attack > enemy attack (if still alive). So brash assault lets slower units get guaranteed follow up attacks, while desperation is what lets them do both attacks uninterrupted by the enemy attack.