I wouldnt say the 1DX is better in every way. Some things to consider against the 1DX
1. Cost - You can buy two or three 5D3's for the cost of one
2. Size - No removable grip so you have to lug the heavy camera everywhere...plus the charger which weighs as much as the camera
3. Noise - The shutter is very noisy. Even in single shot it will turn heads. In drive mode it's a machine gun going off. Scared off a lot of ducks with that one.
4. Shorter battery life - 5d3 with one battery will last longer than the 1DX. Add the grip to the 5D3 and you may last a week of pretty heavy shooting before needing to charge batteries.
5. 1DX cannot run Magic lantern. 5D3 can, adding a lot of additional capability such as one shot HDR (Dual ISO), focus peaking, intervalometer, ETTR and more.
6. 1DX is 18MP. Not much smaller than the 5d3's but if you end up cropping you will notice it.
I opted for the 5D3 and have used that for pretty much everything from landscapes to pro sports...now that I have the 7D mark II, I also have the FPS and AF system to help in that regard. Oh and between the two I spent less than that of one 1DX.
Many people would say point 2 is a plus rather than a negative. I like the build, size and weight of the 1D X. It balances perfectly when used with big whites. Plus you cannot forget the grip at home, one less thing to worry about.
Are you sure about point 4? I would be surprised if that is true. Even if it is, I doesn't make much difference. I forget how many thousands of pictures I can take with just one battery, my spare hardly ever gets used.
As for point 5 - could be a plus or minus depending on your point of view. I do not have any desire to install Magic Lantern, I doubt I am the only one.
6 - nah, you won't.