runakid wrote:
Why should I switch from my Nikon D800/D500 to a Z9?
What will I gain?
Here are my opinions and everyone will have different ones.
As a manufacturing engineer, I think the camera companies saw mirrorless cameras as a means to simplify and reduce costs in the manufacture of their cameras. This was an opportunity to eliminate the moving mirror assemblies, a source of manufacturing costs and complexity. Also, as you may have noticed, there is a tendency toward the use of electronic shutters, also a complex mechanical assembly.
There were other reasons also. The mirrorless designs also facilitate faster shooting or frame rates along with video since the flapping mirror is no longer a factor. Video capability has become a major driver in consumer use of cameras. Unless you are shooting video exclusively, the use of purely video cameras in the consumer market has virtually disappeared.
Also, since cameras have moved to be more "electronic" rather than "mechanical" improvements, updates, and even additional features are easier to add through software. This has been a trend in electronic equipment for years. The camera companies were late to the game in this respect.
The only real reason I see to change from the cameras you now have to a mirrorless is to gain advantages such as better focusing, video, or features you do not have now. Otherwise, I do not feel there is a real quality in image quality gained. Of course, this comparison must be made in equivalent systems e.g. resolution, lens quality, etc.
Like computers, cameras advanced quickly as they moved to be more electronic than mechanical. Camera makers were able to add more features for less money. This trend will continue, just like computer and cellphone technology. Consumers pay less money for more capabilities than was possible with the older designs. Did image quality actually improve that much? I doubt it. Personally, one of the reasons I like the newer designs is the auto-focusing and stabilization technologies that are available in many of the mirrorless systems.
So, the short story is, if you like the images you are producing now, I see no reason to change. If mirrorless allows you access to features that you need or want, then make the move.