Yeah, it seems simple

Then companies start quibbling over what software is required for the system to function, so much that the courts give up trying to fight them

Simple: Anything required for the hardware to function must be open source and user replaceable (no signed firmware, or at least a way to turn off signatures or load your own keys).

the “software” is a single unit, the whole TV OS. I don’t think any vendor considers the homescreen of the OS a removable app besides perhaps Android. Certainly not Samsung lol.