Dayo is an entirely different type of pircha; I probably shouldn’t have even called it a pircha.
Dayo limits the extent (or possibly, as in this case, the applicible cases) of a k”v. IOW, it doesn’t challenge which is the kal and which is the chamur, it limits what we can learn from the k”v.
A pircha shows that which has a tzad chsmur also has a tzad kal, so meiheicha teisi to follow the tzad chamur; maybe we should view it as a kal.
Again, the kal and chamur here is the rasha (Achitofel) vs. an ordinary, non rasha, equal who taught Torah. A standard pircha would be to show how there’s an opoksiree aspect to Achitofel, but that’s not what the dayo does; it merely limits the effects of the k”v.