It's not only a matter of bandwidth, but a matter of CPU utilization. I've tried to feed screenshots to ffmpeg and other tools, and it's just... unusable. It works, but consumes way too much resources. At least on my computer (MacBook 13-inch, 2019).
So from on side you have CPU utilization, from the other - network. Network is cheap, but encoding is expensive. This is my thinking at least. I don't have proof - only local experiments, but it's a really good idea to start measuring this.
I also have other ideas in mind on how to scan the screen and send only parts of the screen that have been updated. Probably if I send only a half of the screen, it will beat the video encoding in terms of network. The diff algo should be very fast though, since we're dealing (in case of 1280x720) with 1280x720=914400, 914400*4 = 3.49 MB info processing in 1 second.
Also, curious to hear about video encoding efficiency vs 60x JPEG creation. Is it comparable?