Yeah, Raiko became really suspicious when he insisted on this. Raiko is supposed to be really intelligent, but to even suggest someone as intelligent as Oshutoru pull off a suicide assassination attempt is not too believable.
On top of this, it seems really off with the "unanimous" decision by the Eight Pillar Generals. There is no way all of them would agree to this, unless they are truly quite foolish. There is something really wrong going on.
Although I feel the Yamato forces got what they deserved, to be fair, the fault fully lies with Yamato's emperor. He ordered the invasion, so blame squarely lies on his shoulders.