If your use case is "watching things purchased/rented from Apple (movies, shows, or TV+ streaming)", it's likely that what you'll see (all you'll see) different by using an actual ATV4K is a pleasing uniform interface and faster response. That may or may not be important to you - your call. (Select Samsung TV's can also now use the Apple Music app for access to music, the Apple TV app for smart TVs works on more different devices, but it's still a modest list.)
But the Apple TV app for smart TVs is not the same as a physical Apple TV - far from it - rather, it's the rough equivalent of the "TV" app that Apple provides on the physical Apple TV (I really wish they hadn't reused the name so many times - makes discussion difficult), which can play Apple content, and gateway through to other streaming subscriptions. And allow you to purchase such content. And that's all. It's basically a vehicle to allow rentals/purchases of movies and tv shows from Apple, as well as subscribing to their TV+ service.
By contrast, an actual hardware Apple TV (the latest is the ATV4K) runs tvOS, and can run all sorts of apps - streaming services, games, music apps, and such - including Apple's Arcade gaming subscription service. Practically every TV station/network has a streaming app that lets you watch their content on demand (if you have a subscription specifically to them, or a corresponding TV provider subscription). There are apps like Plex, Infuse, and VLC that will let you stream content from your own home server (which could be a NAS, Mac, PC, etc.). A lot of people use those with a local NAS in their home to store all their movies, rather than having to get up off the couch and search for the right BluRay. It also does HomeKit, and if I'm watching something, it's surprisingly useful to be able to hold down the Siri button and ask her to change the lights.
Aside from occasionally switching to broadcast TV (for SNL, the Super Bowl, the Oscars, and now, sadly, the daily state/county/city COVID briefings), my TV is basically a monitor, connected to my Apple TV. The TV itself (a 2019 4K Vizio) has a whole pile of streaming clients built in (Netflix and such), but they're all a bit more clunky and sluggish than the ones on the Apple TV (well, my experience with them is fairly limited).
So long as the streaming picture quality is the same (whether it be from Apple, Disney+, Netflix, Amazon etc etc) I'm not seeing any gain. Maybe an Apple TV is slightly nicer in getting from a button press to a video/music track however all of my 4K content comes from a streaming service of one type or other and all have an app direct on my TV. Yes, I have an ATV (albeit an ATV3) but since I got my new TV (Samsung Q90R - would have preferred a Sony OLED but my ambient lighting is too bright for it and I no longer care to be unable to watch TV in the daytime - can't beat the anti-reflection layer in the Q90R at this time) its sitting in its box ready to be picked up by its new owner.
While others may find it fabulous the ATV is no longer for me. It was while my previous TV was unable to do any of the tasks I wanted the ATV for, but with the new TV I have many better things to ruin our environment for. Sorry.