Lord Raine said:
Calling bullshit on the third point. Soukyoku was never said to be equal to a million Bankai's. It was also never said to be equal to a million shikai's. It's likely equal to a million seal zanpakuto.
The wording specifically states that it has the unleashed force of a million Zanpakuto. That's canon. A sealed blade is not "unleashed", no way, no how, not a chance.
The term unleashed force would logically be referring to the output of a Zanpakuto at full power. And the full power of a Zanpakuto would be Bankai. Thus, it follows that the Soukyoku has the force of a million Bankai's.
Also, the very fact that the Soukyoku is only used to execute those of titanic spiritual pressure and power is proof that the force it brings to bare is well beyond what any single Shinigami would be capable of unleashing. It is directly stated in the descriptions and dialogue that the Soukyoku exists to destroy individuals for whom other methods of execution would not work, simply because of the titanic scale of the individual's power. That by itself, if nothing else, affirms the concept that the Soukyoku possesses power beyond what any single individual should possess, barring truly extraordinary circumstances (like whatever-the-hell Ichigo is).
It obviously has some form of sentience, because it is canon that Zanpaktos are sentient, and even discarding that, it it were simply a mindless device, it would not have backed up to make a second attack, it would have just kept going towards the target in a straight line.
Given that it is sentient, we can also assume that it can sense the relative power levels of people/things in its vicinity, which is something that has been demonstrated in canon.
With these two points, we can infer that the Death CHicken wasn't using its full force.
Kenpachi Zaraki doesn't go all out unless he knows it's necessary. The same can be said for most captains/Vice Captains/shinigami/hollows/Arrancers/Tentaclemonsters.
Now, if you had the power of a million Bankai, would you bother to manifest all of that power and use it? Especially if the target of yoru unholy wrath had teh spiritual power on par with a mouse?
No. You'd use a tiny fraction of that power, since wasting all that force on a puny ant is stupid.
No, when a powerful spiritual entity imposes himself between you and the target of your wrath, you would proceed to unoeash more/all of your power, since the insignificant gnat thinks it can stand up against your full power, and you would most likely obliterate him, and a significant portion of the surrounding area, except you got hit by the plot device, and destroyed.
Don't cite me on it, but I think they actually say something about this in the manga. I'll see if I can find it after class.