Heres the thing. I like android tv. But it works more like a phone than a set top box. In this case I just want my apps (plex, settings) to close after i leave them instead of remembering my last location and staying open in the background. I dont want to stop watching a movie in plex and then an hour later come back and be forced to hit the back button until i get to the beginning of the app. I dont want to be in settings leave and then when i come back wonder where the hell i am then have to again backtrack to the beginning. Just like roku (and really every other box) I want each time I open the app for it to be a fresh run.
I was wondering if I could just use a old phone app like task killer and side load it to automatically kill apps. Maybe this is just how android tv will always work, idk. (also if anyone has a fix for google apps playing video in the background and not closing that would be great too.
Both of your requests are going against very basic features and design philosophies of the OS.
Apps suspend rather than killing so that they are instantly pulled back up. Their processes are suspended so they aren't using in resources, and they open much quicker...it's a far better user experience.
As for the Google apps playing in the background, that is so that you don't have to stop what you are watching to pick the next video from your recommended videos.
You're certainly free to use Android as you wish, and I'm sure you can sideload a task killer easily, but why are you using AndroidTV? Just use literally any other device, as you've said?