With Topaz De Noise AI and Sharpen AI software I am able to go into the iso range of 3000-4000 in many cases and still retain good detail even with the 5D MKIV. The 1DX will even go a bit more in many cases especially if the images are for internet presentation.

I have a set 16x20 prints from my Ecuador trip and several were shot at iso 3200 with the 5D MKIV. They show really good details in the birds plumage.

To your point Dave .... post processing plays a big role .... not really skill but great software that's easy to use.