Im sure this is to do with how the game reacts with ping as host there is no delay so the moment one of the arrows hits a storm vermin for example and kills it the other arrows immediately go after other targets but as client they do not react as fast and do not switch targets so 2 or more arrows can hit that target although it is already dead the worse the ping the slower it reacts so it can go from killing 3 storm vermin with one true flight ult as host to only killing one as client this also applies to pyros ult effectiveness
I have to agree with arknox. Waystalker is far more powerful when the player it self is the Host.
This really is ground breaking when u have a character that her most powerful ability is useless.