I moved from an X-Pro2 to the Z6 as a fairly early adopter. As it is, no regrets. The image quality is noticeably better is any sort of difficult lighting and yes, that 24-70 is easily the best "kit" lens I've ever used. I like being able to adapt old lenses at the correct focal length The EVF is a huge improvement on the Fuji and by no means least, this thing has IBIS. I admit that the X-T4 ticks a lot of boxes v the Pro 2 but you still have APS-C image quality. The Z6 is actually often cheaper than the T4 anyway.
On JPEG's, when I tested, was surprised how good they are -- really quite a natural reproduction. But I never shoot JPEG anyway. If you want Fuji colours in a Nikon, one way is to use Capture One and choose Fuji colour profiles. Don't know of a way to do this in LR but don't feel the need anyway. Oh, and another endorsement for the 70-300 AF-P. It would be theoretically nice to have a native as standard telezoom but this is by far the best value I've ever come across in this category -- very hard to fault it except of course it's rather slow. I could be tempted by something at fixed f4.