Being that I'm pretty deep into the Apple ecosystem I'm still very interested in a 4k AppleTV. Even though I have a 4k HDR TV I still tend to utilize my AppleTV 4 at 1080p more than the TV apps and my PS4 Pro at 4k. For me the AppleTV is MUCH more then just a way to watch Netflix, if that is all it did then yes my Samsung TV would be better.
First, there is all the proprietary stuff like AirPlay, TV app, easy access to my iTunes collection, Apple Music, iOS remotes, etc....
Second, homekit hub. While that could fall under proprietary stuff the fact it can be a hub at all is the point. Combined with using "Hey Siri" to turn on lights, adjust temp and stuff is nice. Although turning on lights would be better once the HomePod is released.
Third, 3rd party apps my TV may not have access to like VLC or apps specifically for my NAS. For example I can monitor security cameras throughout my house with their app on my TV. While I don't have a need for it a buddy of mine uses it to see and hear his baby daughters room upstairs while he's in his office in the basement.
Fourth, I just prefer the layout and interface plus its voice control (Siri). While Siri is in no way indispensable the way I use my AppleTV makes it really useful. Game of Thrones title sequence "Fast forward 1 minute 30 seconds" and its gone. I find that much easier then scrubbing through. And its incredibly useful for a show that starts the title a random way in.
Fifth, just general ease of use. While my PS4 Pro and Samsung TV features aren't by any means "hard" to use I don't feel its as fluid and seamless especially when the TV app is accounted for.
Sixth, future app potential. I feel its a platform ripe for future apps and expansion whereas many TVs are stuck with what they came with. Plus the devs aren't as limited when it comes to updates for their apps and Apple is good at handling the update implementation.
While I understand the AppleTV isn't the best solution or even a good solution for many people, for me a 4k AppleTV would pretty much remove all its negatives and clearly stand above all other options. And while I would like other things too like full pass through of any and all audio codec I can deal without.
I don't want to sound like a paid shill though because its not all good. The remote can be finicky and its incredibly fragile. Apple has their own restrictions especially when it comes to game controllers. Some apps just suck and since tvOS isn't as popular as iOS they don't get updated as often as they need too. And I question the tools and power the devs have over the OS itself sometimes. For example...
There is STILL no refresh button in the YouTube app. My subscriptions put up new content and closing the app and reopening seems half baked. Less than half baked actually, its like they completely forgot.
The new Netflix app does that live preview thing like my TV but its not very fluid (not that I like it, I find it distracting).
Hulu app used to crash all the time. Got rid of Hulu so it might be better now.
Certain things make me wonder if its the devs inexperience, not caring due to the small user base or just limitations of tvOS itself.
At the end of the day even after attempting to replace it with other devices I keep coming back and for me its price point is currently very reasonable for the amount of stuff I use it for.