- Faster, smoother interface due to a much faster CPU
Literally no difference between my ATV4K (previous version) and my LG CX. Both are smooth and speedy.
- Tight integration with Apple services and devices
While I realize this varies, my LG supports both HomeKit and AirPlay2, and has an AppleTV+ client that is identical in function to the one on my ATV4K.
- You can use iPhone as a remote in a pinch
Thanks to HomeKit integration, can do the same with my LG.
- Availability of some games, including most Apple Arcade games
Point to AppleTV, although Smart TVs are starting to add game streaming apps. Which, of course, Apple doesn't allow.
- Wider selection of apps (NBC, ABC, Crunchyroll, Plex, CBS News, you name it)
Varies based on SmartTV manufacturer, absolutely. Any TV running GoogleTV/Android will have all of the same apps as the AppleTV does. My LG's WebOS has every app I commonly use on my ATV4K, and many more, although again, I fully admit this will vary based on individual needs.
- Now, the usability and convenience of the remote is far better than you'll find on any TV remore
Personal preference. I'll take my LG's magic remote over the stupid, worthless, die-in-a-fire Siri Remote any-day. But looking forward to picking up one of the new remotes as I suspect it will be much better.
- Cast audio to HomePod stereo pair via AirPlay
Given the HomePod Maximum is now discontinued, I don't know that I would trumpet this as some kind of tentpole feature. But yes, if you have two HomePods, this is a nice bonus.
- AirPlay screen mirroring has significantly less lag and significantly fewer compression artifacts on Apple TV versus a smart TV
Have not noticed any problem or difference with AirPlay-ing directly to my LG versus my ATV4K. Obviously, if you buy some $200 WalMart special TV, you get what you deserve, performance-wise.
All this being said: My point was not to rag on your post, or on the ATV4K. I like mine very much, despite having a very capable TV. But I also wouldn't call it an "essential" device. I bought it back when I had a much older TV that didn't have any smart capabilities. Now that I have a modern TV, it would be hard for me to justify buying an ATV, especially since I also have a Switch and an XBox Series X, the latter of which also serves as a perfectly adequate media box (although I'm not a huge fan of using a game controller as a remote).