Math is off a little. Cropping by 1.6X to the side on the 5D4 will give you 11.7M pixels on the same subject that the 7D2 can put 20M pixels on. Remember, you have to divide by 1.6x1.6 = 2.56. If you had a 5DSr on the other hand, what you say is going to be true.
I have to agree, my bad. I don't know why I did that (I am usually good at math) - I somehow decided that the 1.6 factor was the area, not a linear dimension.