The current Apple TV is, in many respects, unbelievably bad, and it has nothing to do with the CPU.
Open up the YouTube app and try to navigate the UI. It’s okay but not really up to the Apple standard. Now try to enter text in the search bar. A nearby iPhone will helpfully offer to let you use it like a keyboard. You get a text field, and you can type, and keystrokes are slowly and not entirely reliably propagated to the TV, but text does not stay in sync. And after a few seconds, in the middle of typing, the TV will decide you’re done typing and move focus to a search result, and the phone won’t notice, and it gets completely desynchronized.
The YouTube app has never been good and never felt like a native app -- it's a wrapper around web tech.
More importantly for games, though, is the awful storage architecture around the TV boxes. Games have to slice themselves up into 2GB storage chunks, which can be purged from the system whenever the game isn't actively running. The game has to be aware of missing chunks and download them on-demand.
It makes open-world games nearly impossible, and it makes anything with significant storage requirements effectively impossible. As much as Apple likes to push the iOS port of Death Stranding, that game cannot run on tvOS as currently architected for that reason.
Open up the YouTube app and try to navigate the UI. It’s okay but not really up to the Apple standard. Now try to enter text in the search bar. A nearby iPhone will helpfully offer to let you use it like a keyboard. You get a text field, and you can type, and keystrokes are slowly and not entirely reliably propagated to the TV, but text does not stay in sync. And after a few seconds, in the middle of typing, the TV will decide you’re done typing and move focus to a search result, and the phone won’t notice, and it gets completely desynchronized.