It's funny to me, thinking back to 1980 when I was a teaching assistant for Reagan Bradshaw and Charlie Guerrero's commercial photography classes at the University of Texas at Austin, that no one at all talked about camera brands; all we really talked about was lighting. How to light. What to light with. How to modify light. Why to make the light on our subjects look a certain way. We mostly defined our styles by our approaches to light and lighting. Now we seem to have collectively abandoned our pursuit/understanding/appreciation of light and lighting and lean mostly on trying to capture whatever circumstances have provided us. It's kind of lazy and kind of stupid, if you are trying to earn a living as a photographer (or videographer) and you want to differentiate yourself from the vast hordes of people who are also trying to become photographers.
This is just one small post and I can't teach much about lighting here; other than trying to get across that I think understanding how to manage or create lighting is vastly more important than whether the camera you choose has 12.8 or 12.9 stops of dynamic range. But I can ridicule you for continually spending mega-dollars on soon-to-be-obsolete cameras when the purchase and mastery of a handful of lighting instruments (which, really, are never obsolete) can make you a much, much better image maker.
Once in a while you might be able to wait around for the light to get neat and you'll trigger the shutter just as golden hour becomes platinum hour and the light gets so neat that you think you are going to wet yourself, but if you do this (commercial photography) for money the real trick goes beyond recognizing that "once in a lifetime natural lighting" and heading over into the productive camp of people who can make lighting absolutely fabulous on command.
My first recommendation would be to read up and understand the logical underpinnings of controlling light. Buy your own copy of "Light, Science and Magic" and get reading. Don't depend on watching endless YouTube videos about how hacks light and they try emulating them; most of the stuff on YouTube about lighting is worthless dreck. Thirty minute of mindless chit chat for about thirty seconds of barely usable lighting tips. Just read the book and start experimenting with real lights by putting into practice what you've learned from the book.
My second recommendation is that you buy a continuous light (a cheap tungsten work light at Home Depot is fine) and then experiment using it at every conceivable angle in relation to your main subject. See what happens when you move lights up, down, to the side, etc. Then experiment with modifiers. Start with small umbrellas and then get bigger and bigger and bigger. Umbrellas are cheaper than workshops. Buy umbrellas from 32 inches in diameter all the way up to 72 inches in diameter. Put the light into them so the beam fills the entire umbrella and then marvel at how different a small umbrella, used at six feet from a human subject, looks when compared to a 48 inch, 60 inch and 72 inch umbrella. Then see how each umbrella's look changes as you move it closer and further from the subject.
Lighting is a life long learning exercise and I'm not about to tell you everything I've learned over the last 40 years here on the blog. But if you don't pick up a light or two or three or four and get started you'll never master a look that you love and that you can create almost anywhere. The beauty of lighting instruments is that the basics don't change based on the price you paid for a light, nor on how ancient the light fixture might be. Doesn't matter if it's Chinese or Swedish. Once the photons leave the light source they don't remember where they came from.
The web is heating up now with discussions about what might be in the new Nikon. There are dozens of videos by self-proclaimed experts who are comparing $3300 cameras to other $3300 cameras. There are a million sites trying to suss out the minor differences between lenses. But the reality is that none of this is meaningful if the lighting you shoot in is ugly and plodding and....boring.
I may change systems more frequently than you change your Depends(tm) but what doesn't change is my appreciation for lights and lighting. I buy cheap lights and I've owned expensive lights; coming out of a good umbrella they are all perfectly usable. The real things to invest in are knowledge and experience in making the light your bitch. No one gives a shit about your A7Riii or your D850 if you light like moron. No Otus lens will save you if you can't create a great look with a good fixture and well chosen modifiers. It's all excuses and credit card abuse unless you follow through and master the light. And nearly all of the professional digital cameras made since 2008 are more than adequate.....as long as the light is good.
I once met a guy who could light with a bed sheet and a 100 watt lightbulb screwed into a twelve dollar work light fixture. He could shoot with a Canon Rebel and a kit lens and his images would absolutely mesmerize and gob smack legions of hacks who were shooting in poorly made light with the world's best cameras. Don't be part of the legion of hacks when a little bit of brain work and some evenings experimenting can get you closer to the amazing guy spectrum.
Decent cameras and great lighting beat the crap out of perfect cameras and shitty or indifferent lighting. Every time.