You are missing the fact that Ken is shooting jpeg and that he is not using DeepPRIME. The beauty of DeepPRIME is that it acts on the RAW data and helps, not just with noise reduction, but also in preserving detail.
The D850 is the same sensor size as your D780.
But, for the work I do, 25k is not something I use often. Even 10k is mainly reserved for concert work. But, no matter what, I can assure you that you can quite easily use 10k on your D780 without much problem. Search for any of the jazz photos I have posted, like here…
Shot at 10k with no discernible noise and no loss of detail