First off Asmo has more experience channeling than all of the Asha'man combined. He was alive for centuries before the Sealing of the Bore. Second, the Asha'man were being attacked by multiple attackers, which is a lot more difficult to defend against than a single attacker. Third, there are multiple examples of channelers defending themselves from people they see with knives. Rand easily stops a Grey Man in LoC and stops a thrown knife from Bashere at short range. Semi does the same when Min throws knives at her.



Again, you're wrong, Be'lal's death is described in a very similar manner, "Before it(balefire), Be'lal became a shape of shimmering motes, specks dancing in the light for less than a heartbeat, flecks consumed before his cry faded." So it could have easily been balefire, in fact comparing the two deaths and the fact that the DO couldn't have brought Asmo back even had he wanted to points very strongly to it being balefire.