Your only looking at this from the most basic perspective that as alternative to the free apps on your 4K TV using Android, Tizen, or WebOS as examples. They are all separate apps there is nothing that makes it easier to manage their usage. Your omitting the role of where a source lies with a home theater setup, the TV is the last of the chain rather then the first. You don't need to worry about that your TV supports eARC, instead its a source that goes to the AVR where the audio is best decoded and makes use of the Room EQ/Calibration while the video goes to the TV. There are a lot of people that hardly use the built in TV apps because of this changed role of what the Apple TV 4K is about. Of course it can act as a airplay device, but its more about its ability to correctly output HDR10 and Dolby Vision streaming content in the bast manner.
One of things I most like about the ATV 4K , is it supports all the mainstream hosts, not get in contract battles like Roku where streaming hosts drop their app agreements.
The chief difference between Apple TV 4K and anything out there is that its doesn't become obsolete with time, I have a older HD and the various App developers continue to keep modernizing their interfaces as tvOS gets new releases. Comparably using Samsung as a bad example your 4K set gets older and they stop supporting apps for older models.
The last three models are still quite actively supported, I daresay you find any Roku that reeks both hardware or software quality comparably. Yes I am a past Roku owner.