It definitely depends on the type of CPU/GPU used, as well as the amount of RAM, the speed of the internet connection, and how much of a load there is on the system. For example, I evaluated several low-end 4K Google and Roku TVs from TCL and Hisense, and noticed that some of the TVs had a very large lag in the UI response while streaming a 4K video on YouTube. However, with 1080p content, things were not so bad.
I did an AI query on the subject, and it indicated that stand-alone streamers and smart TVs are both equipped with a single System on a Chip (SoC) that integrates the CPU and GPU. It listed the following additional functions used to manage the TV set:
Picture and motion processing
* Picture upscaling
* Motion handling
* Image enhancement
Hardware management
* Internal tuners
* Multiple inputs
* Audio processing
