D850s may be stuck in 2017, but that is a great place to be stuck as a DSLR. I trust my D850 over any of the mirrorless cameras I own! It is big, it is heavy, it is responsive, and it delivers for me. There is nothing magic about mirrorless cameras; they are energy (battery) hogs. Newer doesn't mean better.
A D850 is plenty good enough in the right hands!
I own a D850. I don't believe that there is any camera in their lineup that is better for landscapes and family related photos. The IQ is stunning. On the other hand, if your goal is BIF or other action photos, the faster frame rates of their mirrorless cameras (especially the Z9) offer some advantages. Also, the D850 is woefully inadequate for video. Unless you use fixed focus, it continuously hunts when following moving subjects. The contrast detection focus with the mirror up just sucks. The fact that you can't use a viewfinder when taking video means holding the camera away from your body to see the scene you're filming, and I have found this to be less stable than using a camera or camcorder with a viewfinder that is held to your face with your arms braced against your body. This is what being stuck in 2017 means.