How much is your time worth? Apple TV is the best experience (not even close to FireTV) for the cost of it. There are ways to get completely ad free if you have time. I've been using a HTPC for close to 20 years for example.
I think that if you want a modern 70+ inch screen I am not sure that plugging anything into and HDMI input will do it. You need to lobotomize the TV. I could be wrong. I am probably going to explore this to some depth next year.
Depends on the TV brand. I use an LG OLED TV and it’s 100% fine being used as a “dumb” TV. I keep it disconnected and use an AppleTV. I never see the TV’s operating system unless I want to adjust picture settings.
How much is your time worth? Apple TV is the best experience (not even close to FireTV) for the cost of it. There are ways to get completely ad free if you have time. I've been using a HTPC for close to 20 years for example.