i think youre missing the point, when obito goes intangible the jutsu is not applied over the enemy instead hes using kamui over himself, so whatever phases through obito even totsuka blade is not touching obito whatsoever, is like totsuka blade was touching simple air, totsuka blade to seal something has to touch it and there´s nothing astral in touching simple air, besides your basing the discussion on a feat never seen on manga panels is like DBZ that freza was said to be the most powerful being but them turns out we also had king cold,cell majin buu, besides do i have to remind that amaterasu was said to not be possible to put out till it completly incinerates the subject? but hey jiraya put out amaterasu and sasuke too, remember every technique has a weak spot itachi said so, totsuka blade is not unbeatable