This is mostly an "eye of the beholder" question. Asking Apple people if you should buy something from Apple vs. enjoy something from anyone else is almost certainly going to get you a bias to the former. So far you've seen pretty measured responses... but the crowd here seems to be VERY Apple-centric... no matter what.
Conceptually, a Netflix-type app on AppleTV and a Netflix-type app on a TV is going to be serving up the EXACT same file to your TV. Conceptually, if there have been no corners cut by programmers, how each system processes that data stream and displays it should have no noticeable difference. Conceptually, if the hardware inside the TV is at least as good as the hardware inside the AppleTV (a < $200 retail device), there should be no advantage of the latter over the former (if anything, it should probably be the OTHER way). You have no way of objectively testing all those "conceptuallys" but subjective judgement head to head. And much like how most home electronics are sold, if one has settings jacked a bit more than the other, it very well may look better or sound better only because of settings differences.
If quality is the goal, bypass streaming hardware as much as possible because streamers are usually pinching the detail to fit their stream into the smallest bandwidth pipe they can (to sell and retain as many people as possible- even those with SLOWER broadband). Streaming is subject to business pressures of lowest common denominator.
So if quality is king: 4K UHD blu ray (and 4K UHD discs), a good outside antenna, etc should be in your set up. If you are in an area already broadcasting 4K over the air, be sure you have a (antenna and) 4K tuner to grab those signals.
Also, check bigger name apps for better streams. For example, I get FOX over the air, via cable AND via the FOX app. But only the latter is delivering select games- such as the World Series and some NFL games- in 4K. It's noticeably better quality than the other 2 options limited to 1080i and some kind of extra-compressed 720p (thanks for the re-processing Comcast) signal.
I hope this is helpful. I'm a MASSIVE AppleTV fan myself and have one hooked to EVERY TV in my home. But if I remove everything it offers except picture quality from the equation, I probably don't need them. The rationale for it is probably much better realized by looking at the rest of what it can do. For example, is there 1+ app you like/want NOT available from the LG app store? Is there 1+ bit of functionality it delivers NOT available in the TV apps, including the AppleTV+ app? Etc.
