This is where I'm at too, really wish Apple supported passthrough. The Shield continues to work but it's a bit sluggish now and needs a new gen.

There are comparable devices like Ugoos (am6b+ with coreelec) and Zidoo but they're a little sketch compared to the aforementioned...

Yeah, exactly. I've looked into those boxes but have steered clear for the same reasons. For now I use ProjectIvy launcher for a very clean launcher experience and I used a custom Shield script someone had posted on Reddit a while back to remove a lot of Google bloat and the Google launcher. Works well enough, but frame-rate matching still requires manual intervention (I have a button mapped to forcing it) and the Apple TV app isn't quite as smooth in playback as it should be on the Shield.