I've had my 7QF 65inch for just over a month. This was a replacement for a new Samsung KS9000 that also had screen issues.
The vertical banding is quite a pain and getting really noticable now under certain conditions (HDR 4k content with darker scenes). Seems to have got worse as time went on.
I also have noticed a grey uniformity issue: starts on the on the far left and runs to the near center of my screen which appears visable during bright scenes, so between both these issues it's getting very disracting. Not happy considering the money I've paid.
I'd love to have contact from support regarding a technician visit please.
Two things I am a bit surprised you were only offered the Q7F for the KS9000. I think the Q8F was reasonable like for like. I had a KS9500 which had recording issues and miss-selling due to the Smart Connect Dongle and Samsung agreed to replace it with the Q9F. Was very disappointed and the same issues as you are having. The KS picture was good and HDR was amazing with Netflix. The Q9F was dull and when there were black bars there was clouding around the corners. There was massive blooming and banding, I showed pics on here and everyone agreed. I sent pics of the Netflix Star Trek which was awful to Samsung and they said it was within spec. The next paragraph said they would give me a full refund, which I got last week.
well they offered me at first the MU9000 believe it or not. That's the first thing they offer for any previous owners of the ks9000.
When I refused the 7QF was put on the table if I paid a bit more. To be fair this is from the retailer along with Samsung.