Did you note that the M6 manages over 40% more pixel per second throughput than the 1DX II?
How do you calculate it?
If you are referring to the 30fps raw-burst mode, that seems to be in some kind of "crop-mode". But I haven't seen any info how big that crop is.
And btw, the spec-shet seems to says 23 fps, not 30fps?
4K video seems to be recorded at some (unspecified) lower resolution and upscaled to 4K output. At least that is how I read the small print.
But "new technology" is of course also always a relative term. It IS a new sensor, and it should have some improvements of various size and importance.
In general I think it looks like interesting cameras. The 90D seems like a great update to 80D. But even though I will consider purchasing 90D as a secondary camera with other strenghts, I still can't see it as a 7DII replacement.