Well I have both - have had the Z50 for a long time now and regret buying it I should have sent it back when I could.
Now the a6700 it is by far much better in most every way.
In most but not in every. There is at least one point which is better in Z50. Namely, Nikon Z50/Z30 have the more sensitive sensor, which is noticeably less noisy than that of a6700. I wonder why Sony have not yet released any cameras with this 20MP sensor. I'd like to see it in a future Sony APS-C camera, such as a7000.
I am not seeing it be any more noisy then the Z50 at all. The a6700 files are a little larger so you need to lower it to the same size as the z50 and you see no more noice VS the Z50. Nothing you are going to see any different in a print.
I now have raw support using the adobe DNG converter and the raw files clean up fantastic from the a6700 no problem.
I am not someone that shoot at super high iso in the first place but doing some testing I see no problem.
My Z6 is more cleaner as expected but the A6700 is really no different in use then the Z50 except I like the a6700 color better for skin tones.
I am now going to start using the a6700 on most all our jobs in place of my Z6 something I could never do with the Z50.
Here is a iso 800 photo using the new Viltrox 75mm 1,2 lens on the a6700 this was edited from jpg and its very clean.
Using the right lens I really dont go to super high ISOs almost ever for anything I shoot.
Have not needed to go past iso 3200 for anything or any jobs we have shot. Even at a wedding reception in a dark reception I am only at around iso 1200 to 2000 and using bounce flash. May times iso 800 is all I need.
Got my RX10 4 In yesterday so far I like it the 600mm zoom is quite amazing even at iso 1600 and 600mm its very usable dong some testing last night. Will shoot some more today.
The viewfinder on the RX10 is much nicer then the one on the A6700 or Z50 its large more like the Nikon Z6 view.
--
Started shooting digital back with the first 2MP cameras. Over 20 cameras later still going. I shoot for a living - family and people portraits, weddings, Sports and a little of everything.