Maybe I can help having exactly the same problem with the same camera Nikon D810. I did a lot of research into this looking at several options. Eventually went down theMFT (micro four thirds) route, and the best decision I had made in many years. eventually P/X all my camera gear with
Park Cameras and bought the Panasonic G9 with the kit lens 12-60mm f2.8-4.0 . Then the Panasonic G9ii came out so bought that as well. it is mainly the lens weight made the difference for me. Even the big Panasonic 100-400mm lens (200-800 in ff terms) is not a problem the Dual image stablisation on the G9ii and the Panasonic lenses working together was the deciding factor ,supposed to be the best.
Personally I would not touch Sony being very dissapointed with the brand and cameras from past experience.
You mention about extensive menu system ? wrong way of thinking if I may say so. Every camera you can start off in auto mode and let the camera do the work
Then after getting used to that then each individual item it the menu bit by bit and don't look at the whole and panic. If you don't use everything in a large menu or not it is there if you want to and not go later on looking to buy a camera with more features.
Then if used or not the video side of the Panasonic G9ii is truly amazing even at a very low 300 fps far slower than most cameras
straight from pan G9ii camera no editing
View: https://youtu.be/7DzwpPB3Vds
Needless to say I am now a huge fan of the cameras I mentioned above ,also being to update firmware on line via
av.jpn.support.panasonic.com
which other makes don't always make available without a fee