This is why I don't immediately jump off the Apple bandwagon like some others here appear to be doing. Over the years of using Windows machines I've learned that specs never tell the story and only are posted to spark the interest of the usual spec-jockeys.
Sure, the new FireTV has voice assistant, but doesn't it offer all the good functionality as Siri does on the new TV? That's yet to be seen.
Sure, the new FireTV has a UI, but it as intuitive, beautifully detailed, laid out nicely and simple to use as the new TV? That's yet to be seen.
Have you used a current FireTV? They have a very slick interface and the voice function already works extremely well. I found it to be an equal device to my Apple TV and use both regularly.