I think the explanations are relatively weak - I've never been convinced that Slayer had the motive, capability or the opportunity, nor that given the confluence of the three, he wouldn't have been punished for not attacking Rand. To make the "Slayer did it" line of reasoning worse, we now have examples of at least one, but possibly two Forsaken expressly brought back in order to set conditions to punish them for disobedience and disloyalty, implying that Asmodean was balefired since it seems the Dark One would rather punish his followers than assassinate them.

I don't know - I doubt you could convince me on this because basically I don't really care who killed Asmodean so I'm not emotionally invested in any particular villain and a few better theories linking it to Graendal have been put forth that, frankly speaking, the "Slayer" theory looks like the only reason people latched on to him is because of his nickname and his creepy but heretofore relatively unimpressive powers.