The point is not a server per TV. The point is a home server period!
A lot of Apple functionality works better with one guaranteed alway-on always-running device available (in other words a home server). We already have the first tiny step towards this in having an aTV (or an iPad) act as a HomeKit server. But that's a tiny function, and right now it's not really expandable.
A real home server would have the same ease of use as aTV right now, but, among other things, I could install a wider class of apps, for example HomeBridge or Channels DVR, both of which right now run on my mac mini, but an aTV would really be a better place for them (especially if the experience came with less baby-sitting of the apps).
If you land up with that functionality in more than one device, so what? Transistors are cheap. Does it upset you that there's a ISP sitting on the A8 or A10X SoCs in your Apple TV that never gets used? That only one of your (I assume multiple) aTVs is handling HomeKit?
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That's not completely true. If, for whatever reason, you don't want to buy an aTV right now, can you put up with a month or two of choosing the app on your iPhone/iPad (maybe even a mac?) and AirPlaying it to the old aTV?
It's not a perfect solution (for me the most irritating part is if you pause the show for more than a few minutes the connection breaks and you have to restart it, but it works, and for a month or two it might be bearable.