How can you argue science in a fictional Manga? Due to gravity and the law of mass, Oonoki shouldn't be able to fly. It doesn't apply in the Manga.
The default setting to all debate is that gravity travels at 9.8m/s^2.
Flying is a jutsu, it doesn't change the fact that they would fall at 9.8m/s^2 without the jutsu.
Even if it did, how do you even know the Juubi's tail is more powerful than Kirin? You don't know how much it weighs, or even how fast it was moving. Anything you pull out of your a** is just psuedoscience with no fact behind it.
Ok, here is something I pulling out of my arse, something that you obviously didn't read in manga.
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Can kirin bust a mountain? No. Can kirin cause a tsunami? No. It only destroyed the top of the hill.
Since the Juubi's tail is much larger and heavier than the Kyuubi, it will have much more damage. The law of mass dictates that the size of an object heavily increase the impact caused when going downwards. In other words, the bigger they are, the harder they fall.
So yes, the Juubi's tail is much more powerful than Kirin.
Unless you think Kaiten > Susano'o in terms of defense, Kirin absolutely obliterates Kaiten.
You can't compare Susanoo to Kaiten like that. They are two different types of defenses.
You are really underestimating Kaiten lol. It has been stated that Kaiten is a stronger defense than Gaara's sand, and I'm pretty sure that Gaara's sand was able to tank C3 without a problem.
Not to mention Neji can't even put up Kaiten in time, since Kirin is instantaneous and he will have no idea it's coming.
You are correct, it can't be reacted to because it reaches the ground in less than a tenth of a second. But it can be
anticipated. To use Kirin, Sasuke has to raise his hand and drop it. As soon as Sasuke starts lowering his hand is the perfect cue to put up Kaiten.