Well, the 8k sets are going to be the highest end units so the resolution will not be the reason it looks better. There are too many factors at play. Especially if the two displays weren't in a light controlled room, calibrated, and showing identical content. If that wasn't the scenario, then you don't have enough information.
Not only that, but there isn't any 8k content so something with that resolution would just be upscaling all content anyway. Plus, the HDMI standards change so much that a current 8k TV could end up being like the poor morons that bought the first gen 4k sets that only had HDMI 1.4. Sure, it's supports the 4k resolution, but it doesn't support HDR, 60hz+ refresh, etc. So, yes, it's a 4k TV, but not to today's standards.
8k will most likely have the same issues. Early adopters are beta testers that have to pay. No thanks.