Sony is in another league.
Bigger and better sensor.
Faster and more accurate AF system (borrowed from the A9 series).
Frankly, the long reach claim to fame with other bridge cameras is more of a gimmick.
How many moon shots do you actually want?
Other than that...super long lenses are handicapped with cutting through A LOT of land-atmosphere.
Do I shoot past 600mm? Yes, I do...but with a lens with a 95mm filter size...onto a FF sensor.
It's not the same thing with a smaller lens diameter with a very small sensor (Nikon).
Get the Sony. Pay once ...and be satisfied.

I myself do not own a mirrorless camera , I did for a brief 4 months . Let me explain , I print for a handful of photographers .One particular client bought a new Sony RX10 m3 and spent 5 months trying to use it and missing focus on a lot of images and he got to where he didn't trust it and would always use his Nikon p700 instead . He then handed it to me said I could have it for $500.00 . Myself owning a D810 gave it a try . I was able to get the center focus point to lock on and track and used for awhile but I was not that impressed with the convoluted Menu . I also didn't like the preview of the past image popping up in the viewfinder blocking the bird I was tracking , it took me awhile to stop it from doing that . Another client told Me he wanted to try it as street walk around camera to add to his camera bag with his d850 ..so he now owns it but wants to sell it to get his $500.00 back or at least part of it . He has the same complaint the Menu is not straight forward so is presently trying to sell it . The original owner went out and bought the Nikon P950 and loves it . I print all his work and large canvases up to 4 feet wide and larger . In the past 2 1/2 months he has sold over $8,000.00 in canvases granted some of the images are from his older cameras but a good percentage are from the P950 .It's ISO limit is not the greatest . Have you considered The new Nikon Z50 mirrorless for $856.00 or with a 16-50 and a 50-250 for $1,195.00 I know nothing about the camera perhaps others do .