The A12x would better position the device for Apple Arcade, a subscription service, which is the business model Apple is moving toward. On a practical note, a more powerful Apple TV is needed for 4K gaming, even with the casual games currently available. It’s choppy and not so great, currently.
I just want to point out that, as written, you said the Apple TV has a crappy UI, terrible OS maintenance, app support and near inexistent developer community. I beg to differ; it has a good UI, great OS maintenance, great app support, and a huge developer community. Just about the only bad part is the very awkward remote control.