Literally no difference between my ATV4K (previous version) and my LG CX. Both are smooth and speedy.
One thing I have heard from friends with "smart" TVs is that your TVs processor is usable today, but in 4 years will be junk and the apps will be laggy or will no longer be updated. My bet is the Apple TV will hold up much better in that regard.
Plus you get the bonus of your TV not spying on you. I just added a Samsung 4k TV to my office and it isn't allowed call home, Apple TV FTW!