But on the other hand TV SoCs need to process the video signal at 4k 120hz 4:4:4 without dropping a single frame, although most if not all those tasks are most likely done by an ASIC embedded into the SoC. Would a modern but very cut down GPU be able to do this and also at a low enough power draw?
There's hardware transcoders on the chip that render your video stream. The menu system is just a terribly outdated Android SoC... the latency is entirely from the speed at which it can render the user interface and has nothing to do with how fast your 4K 120/240hz panel can draw a frame.
