Hi!
There are really two use cases you are describing here:
- Settings WLED effects and colors according to some system parameters
- Continuously stream data to WLED (e.g. music reactive)
For the first use case, the JSON API over network is the way to go. One command will typically use less than a kilobyte so it shouldn’t impact your network performance in a significant way if you only update the LEDs every few seconds or so. It also is completely local and doesn’t use the Internet, so if your connection is the bottleneck, it is unaffected.
Although the possibility of receiving JSON commands via Serial is already proposed so it might be coming at some point 
For the second usecase of “live” streaming RGB values from e.g. a music reactivity software, USB makes much more sense as the 30+ packets a second could indeed affect your network if you have an older router. You’re in luck though since the two protocols Adalight and tpm2 are already supported by WLED over USB serial!