Your liking for either EVF or OVF depends on what? Subject matter? Or perhaps lighting
conditions? You mention battery life. Which gives the longer battery life? I can see that the EVF is using battery power all the time the camera is switched on. Is there a difference to how quickly a lens set to AF focusses? Especially in low light or non-contrasty situations?
A little bit of both really. For wildlife I definitely prefer OVF, as you can spend hours just staring through the viewfinder scoping things out. If doing this with mirrorless you have to keep waking up the viewfinder, and there's a little lag with it coming on too. I also find the D850 focusses far more quickly and accurately on birds in flight than the Z6 does, with the same lens.
For shooting buildings I've always preferred using the screen anyway, so it doesn't really matter if your camera has a viewfinder at all in those situations.
As for AF speed, it depends on how well practiced you are with the AF system of the camera you're using essentially. I cut my teeth in photography shooting mountain biking on a D70, so became very familiar with which AF settings got the best results in a whole variety of lighting conditions and speeds of subject matter. The best results will almost always be had when using the fewest AF-points as the camera has to do less processing, but obviously to do that with fast moving subjects you have to know your subjects movements before they're even in frame and how they're going to be composed within the frame for the photo you have in mind too. When using auto modes such as subject detection (eye, face, animal, car etc) mirrorless systems have been pushing the envelope here but ultimately they're still a crutch, and not as fast as using well practiced technique. When using auto modes I find the mirrorless does grab faces more quickly, it's not a particular game changer but it does make it easier not having to think about AF point positioning in some situations.
In low light they seem to focus equally well, however I can find what I see in the EVF to be a bit misleading at times in terms of exposure. Because it always tries to make sure that you can see the image equally well in all lighting conditions, in low light the image you see in the viewfinder can appear very bright and it's not until you clock what the meter is reading that you realise how dark it is or how high it's boosted your ISO. Looking through an OVF you always know what you're looking at, so it's easier to judge your exposure.
I can get about 40-50% of the number of shots on mirrorless than I can on DSLR with the same battery in the same shooting conditions. I can say that confidently as both my Z6 and D850 take the exact same battery, so for fairness sake I tried it out with a brand new battery so that I knew the battery age wasn't affecting anything. Obviously older batteries will not charge to as high a capacity as a brand new one, which is where making a comparison between DSLR and mirrorless can often be tricky if people are comparing a new mirrorless camera with an older DSLR.
