that a guy who got shot in the chest in TAR where he goes to kill wolves for fun can appear out of thin air and kill one of the Forsaken?

Almost everything that leads us to think Slayer MAY be lethal enough to kill Asmo happens in WH. Think it through if you take all knowledge we gain in WH out of your theory Slayer would simply be a pretty normal guy who maybe has a Ter'angreal that lets him enter TAR in the flesh. There is never mention of him having other gifts from the DO and no reason to believe he's anything more than an average guy! There is not a single quote from prior to LoC that gives us any indication that Slayer is any more dangerous than a Blade Master level fighter! Hello, Perrin outsmarted him on his own ground in TAR!