A huge part of why Channels works so well is our custom video player. Switching to the native player is not feasible- we would be starting from scratch and would have to reimplement every feature added to our player in the last three years. Plus, the native player would only work for users who had a suitable DVR server that supported transcoding. Plenty of users use only the Channels app, or run their DVR on older machines or budget NAS with no transcoding capability.
If you want to see how the native player works, try the DVR's web UI in iOS Safari, or try Plex's Apple TV app. It takes 5-10x longer to tune into a channel and there are all sorts of reliability issues. In fact, even Plex is moving away from the native Apple TV player. Emby and Infuse have already ditched the native player as well. It doesn't make sense for us to double the code in our app to try to deliver a sub-par secondary player that only a small percentage of our users will even be able to use.
I know the Airplay issue in this thread is really annoying, and it sucks that Apple hasn't been able to fix the bug in the API we're using. I've been poring over recent WWDC talks about Audio APIs to see if there's something newer available. I heard that Infuse recently fixed a similar issue in their app, so I think there is a workaround available.