A) A TV is "modern" for maybe 3 years, after that it feels slow and sluggish as the apps are developed for faster TVs.Who buys Apple TV when a)virtually every modern TV comes with all of the major streaming apps (and in many cases AirPlay support) and b) you can get a fire stick or Roku for a fraction of the price?
Some TV brands might also have an inferior app store. While image quality might be good enough for much longer than the smart tv part. I have a Full HD 50" Panasonic plasma in my cabin, the smart-tv part was always bad so I used an Apple-TV box even for TV channels and the TV feels like new while its actually 7+ years old.
B) Is it really so important to save 50 or 100$? I mean I would much rather have a box that actually works together with my iPhone and iPad. Like if I have to enter a password to one of my apps on the Apple TV it pops up on my iPad asking if I want to type the password there. I never got this question when I had an Android phone and the same Samsung TV but no Apple TV. I ended up connecting a wireless keyboard to the TV.