I can't say I believe any small-pixel sensor could perform as well as the 1D X.
explain what do you mean with performe as well ?
Well, if you have a 21mp APS-C and an 18mp FF, not even downscaling the APS-C image will normalize noise enough to compare to the 1D X image at high ISO. It has a 91,000 electron full well capacity. Assuming a 21mp APS-C has similar Q.E., a similar CFA, and gets around 27,000 electrons at FWC (similar to the D5200), the 1D X is still going to have a 340% full well capacity advantage. It'll require considerably less gain at high ISO...so, even a fairly revolutionary APS-C sensor design on a 180nm process, even if you normalize the APS-C image to the 1D X image size, is not going to perform as well. The difference between 18mp and 21mp is just not enough for the basic post-process scaling algorithms most photographers have access to to overcome.
Now, if you printed both on an 8x10, the 7D II will have the resolution advantage, and would have sharper detail than the 1D X, and with that much downscaling, the noise and DR differences would be negligible. And, of course, you could print the 7D II image at a slightly larger native size, and if you upscale the 7D II image will retain more detail than the 1D X, even if it appears to be a bit noisier.