There's a reason no one makes a 24-200mm FF lens. Several, in fact.
- The main one is that not many photographers who know what they are doing would ever consider buying such a lens for a FF camera, particularly for one with as high resolution as the D850.
- To get anywhere approaching a constant, usable aperture the lens would be very heavy and large.
- Such a lens would be very expensive to produce at any level of decent image quality.
- Lenses with smaller zoom ratios can be smaller, lighter, cheaper, faster, and produce higher image quality than a larger, heavier, more expensive, slower lens with inferior image quality.
The entire point of an interchangeable lens system camera is to allow you to use different lenses that are better or even great at one thing but unsuitable for other things. Fixed lens cameras force you to use a single lens that is mediocre or worse at a lot of things but better at nothing. Insisting on using a single lens for everything on an interchangeable lens camera is not much different than using a fixed lens camera. In some cases the fixed lens camera may meet your needs better than an ILC with only one lens.
The best lenses are all prime lenses. That means a single focal length. No.Zoom.At.All. They're really good when they provide the field of view and other characteristics you need. This is because they can be optimized to do one thing at one focal length. A good flat field 100mm macro lens is different from a good 85mm, 105mm, or 135mm portrait lens. But they are not very flexible, so you need a lot of them for various different things. Some are pretty good for not much money (e.g. EF 50mm f/1.8 STM @ $120). Others are incredibly good for a boatload of cash (e.g. EF 400mm f/2.8 L IS II @ $10K). Most fall somewhere in between.
Compared to their zoom lens counterparts, in addition to equal or better optical quality at a lower price prime lenses can also be smaller/lighter, have wider maximum apertures, and often still be much cheaper.
Short ratio zoom lenses, that is zoom lenses with a less than 3X difference between their longest and shortest focal length, can also be very good. But the best ones cost a lot.
When you move outside of the 3x limit is when image quality really starts to noticeably go down. Some 4-5X zoom lenses that fall entirely in the telephoto range can be pretty good. But when you start trying to design a lens that goes from wide angle to telephoto and covers a 5X-10X or more zoom range, that is when it really starts getting difficult to keep it affordable and manageable with regard to size and weight and still provide excellent image quality. You'll usually get better image quality and spend less buying something like an 18-55mm and a 55-250mm pair of zoom lenses than you would get with an 18-200mm 'all-in-one'.
The main reason I am looking for this focal range is because I spent several thousands already on constant aperture zoom lenses (the 14-24 f/2.8 and 200-500 f/5.6) as well as a prime (50 mm 1.8) and as a still new and relatively inexperienced photographer, I realized I was missing a big focal range, so I wanted something that could cover it as my photography style and interests develop, after which I can pick certain other primes or higher end fixed aperture zoom lenses. Additionally I was running out of room in my travel case.
If you are looking for a three lens kit to take you from 14-500mm then the real overkill in your kit is the D850. To do 14-500mm with anywhere near the quality to match the D850, you need four lenses: A 14-24mm, 24-70mm, 70-200mm, and 200-500mm. That keeps the zoom ratio below 3X for any one lens.
If you don't need or want quality any better than what you can get with a 24-200mm FF lens, a D600 or other lesser FF camera would serve you just as well for that purpose. By the time you go through the development process you describe in your comment, the D850 will be out of date compared to the newest, greatest, hot off the assembly line Nikon high resolution flagship. (Assuming Nikon hasn't gone under by then...)
