It’s not supposed to grant guaranteed crit chance when battle spirit is active and for other attacks it doesn’t but onslaught hit itself is almost always a crit. In the past several weeks I only remember seeing it not crit once. Crit chance on onslaught in pvp is definitely broken.

@ZOS_Kevin this does put onslaught in an unhealthy place, it already ignores penetration making it hit hard and grants the same effect for a duration which is incredibly strong. But being a guaranteed crit on top enables way too much burst with some builds being able to land 20k+ hits and most builds utilizing it reliably land 10-20k.
It’s only the opening hit that takes away half or more of targets health, followed by another huge burst of damage as the buff is active.