I absolutely agree, and the fact that Apple TV works in such a configuration, but apparently is unable to pair permanently with the HomePod speaks to Apple's complete disorganization around this.
HomePod does persist Airplay connection with AppleTV as long as you don't Airplay directly to HomePod from a separate source. You can still Airplay to AppleTV that is Airplay'ing to HomePod but that will turn on your TV. It's not perfect but I have enjoyed using HomePod as my primary AppleTV speaker since launch and hope they introduce multiple Airplay streams with Airplay2 release.
That's good to hear. One of the reviews I saw said that it did not maintain that connection; maybe that was a bug or I misunderstood.