If you mean by whiffing a heavy with no follow up then it's just a guard switch delay to allow people to follow up with an attack after they miss. With berserker though if you whiff a heavy you can get rid of the recovery frames by dodging and zone attacking. https://www.youtube.com/watch?v=b8yu9lJXWhM . If you skip to 0:15 you can see what I mean after he back dodges after he misses the unblockable. Try testing this out in the training to get a feel for it