What are you streaming it through? I bought a newer roku stick last month and it's pretty sharp (on my 13 year old panasonic).Started watching Wheel of Time, though I've never read the books. I had to cut back the resolution to 1080p, because holy shit, streaming 4k looks terrible, even on my fast internet.
1080p keeps the backgrounds from worming out on my roku stick, at least.
I should install the other Roku on the newer 4k downstairs and watch the shitshow!