Well I did a comparison to an iPhone SE 2020, and I have to say at 1080p60 they seem pretty much the same. After a few reruns of the same video I do agree there is some microstuttering on the RN8 that is not shown as dropped frames but it definitely very rarely compared to the entire clip, you could get dropped frames on higher resolutions but those are noted in the stats. So in summary I am not sure whether you are referring to this from time to time stuttering or you have a more overall lag you experience in watching a video. I tried to compare to something I know will work and yes there are some quality reduction but we are speaking about a device 4 times as expensive.
If this is not present on global then that is something Xiaomi did wrongly on betas and it wouldn't be the first thing but it is probably nothing that could be fixed by the team since it is remarkably difficult to see yet alone do something about it assuming there is a difference in the first place. One last thing comparing two devices there are many variables to note if one has more running apps, syncing, finishing updates, etc. You have to factor that in as well, not saying that you didn't just noting it.