Isn't the strength of the nino determined, to a certain extent, by the strength of the walker cell? This has always been forecasted to be a weak nino to perhaps moderate. Having the walker cell weaker shouldnt be a surprise, right? Would think that other factors, as you noted, would have a greater chance of affecting the cold season pattern than if we had a solid mod/strong ninio throwing it's weight around.
eta: I'm honestly questioning because I dont know....I understand very little about what HM posts some times.