This week, YouTube pushed out version 1.01.04 of the app for Apple TV 4th and 5th generation devices, and it addresses a few of these user concerns. The major update is a "modified" subscriptions tab that nixes the long horizontal list of subscribed YouTube channels -- which made it take much longer to get to channels at the bottom of the alphabetized list -- and reverts back to a grid layout akin to the original app. YouTube said this was done for "easier channel selection."
Although it's not mentioned in the update notes, one user on Reddit said that there have also been a few tweaks to video scrubbing, so users can "go through the video with the touchpad again instead of slowly rewinding/fast forwarding." When doing this, thumbnail previews of the video pop up to give you an idea of where to land as you jump through the video, but YouTube still doesn't use Apple's systemwide playback UI and there isn't any support for quick 10-second jumps forward and backward.
Otherwise, YouTube said that the update fixed an issue with the search keyboard when people were using "non-Siri TV remotes," and it includes the usual bug fixes and stability improvements.