Whether I switch from my D780 or just add one, which camera is considered the best for overall focusing abilities? I may even switch brands someday so I’m open to all brands. I shoot all kinds of things so it ranges from wildlife, to macro, to landscapes. Frankly, I’ve always had bad eyes and they aren’t aging well.
Thanks,
VinnyH
I think you should sit tight until you have a clearer idea of what performance you need and why.
The D780 is a good DSLR, but it's not cutting edge in terms of AF performance. It's essentially a Z6 in a DSLR format. The Z6ii is a small upgrade plus provides mirrorless. A D850 would be a step up in some ways, but a step back in others. The Z7ii is a step up in most areas but also increases resolution. In the mirrorless arena, the upcoming Z9 based action camera would fit well with your current lenses. The Z6ii and Z7ii are perfectly capable cameras for action, but not "action cameras" in the typical sense. For most situations, those cameras are more balanced.
Are you looking for an action camera specifically? That's not what you said, and your current gear is not action oriented - it's a nice balanced kit.
Are you planning on upgrading lenses? That will take you out of a $3000 budget range. Of the lenses listed in your signature, the 150-600 is not particularly fast focusing for action and there are better options - with a price tag. There is a lot of difference in lens AF speed - especially when you look at newer lenses designed for that purpose.
Macro and landscapes don't require fast, action oriented AF. There are other features that are a lot more important. How big a part of your photography are those genres?
My initial reaction is changing brands is an $8,000-10,000 decision to maintain the level of equipment and performance you have today. You'll get some upgrades with the right newer gear selections, but only if you are targeting the right features for your needs. If you gave me a $5000 budget right now, I would not spend it on a camera body or switching systems.