It is because of Riboku knowing & even explaining how important such a rate of successive attacks is that makes me wonder why he is so surprised, or, concerned. He screwed Yan/Qin by killing their heroes, went into Qin court, challenged everyone and their gradmother, spent a year fortifying the western front and now gets cold feet with Ordo stepping by from the east? For the smartest person and god of prep this seems rather odd. Even while sharing a border with everyone and having poor personal.
To make a long story short: Yan seeking revenge should have been taken well into account. If it was Karin at the doorstep, suddenly deciding rather to snack Zhao than keep Qin in check, I would cut Riboku some slack.