I’ve had Nikon cameras since 1990, except in medium format which are Mamiya.
One advantage Nikon has on non-Z bodies, is the older glass (dirt cheap and ED glass is excellent), while not automatic, WILL work on DX (with cropping effect) and is FX format (24x36) just in manual mode. (Note: I shoot primarily portraiture on a stand, so make lots of manual adjustments anyway) . If you are into micro photography, Nikon has some bellows attachments that will take you over 100X.
FX has more light since it has a larger sensor, so you either get more light for the same number of pixels, or more pixels with equal light compared to the smaller DX sensor.
I have Nikon bodies with DX senors, but if I get a good buy on an FX sensor I’ll by it because if I upgrade to a FX senor body - which I intend to be on my next upgrade, I can still use all my lens with it. FX lens also give full coverage on my film camera (I like film, especially Tri-X) DX sensor does crop it, but my investment in glass is multiples the cost of a body.
I looked at some Z bodies in early November. They are nice smaller form factor in both the body and the lenses. BUT, they require all new lens since non-Z lens won;t work on it. Whatever the advantages are of the new body, the benefits don’t are very minimal FOR MY TYPE of photography. For other people that want to start over on basically body and lenses and have the scratch - go for it.
When I started out in photography, the advice I got when ordering a new system was: Spend more on lenses than the bodies, bodies will always be upgrading - lens can be used on the new bodies. Nikon has been really really good about backwards compatibility between Analog and Digital, and between types of lens in digital, e.g. whether motor is in body or in lens - they can still be used but some automatic features may be off.
My strongest advice is, if you are going to spend serious money on cameras and lens - deal with photo shop where you can get the advice first hand. In the long run as they get to know you, they’ll keep you from over buying.
I confess, I’m not familiar with the nuances of Cannon; Fuji great scientific line in both IR and UV for forensics; Sony (although when Fuji and Sony first came out they were compatible with the Nikon mount). So others can speak to those. Cannon went aggressively into massive fast lens for sports.