The bottom line is that TCP CUBIC is actually pretty bad for reasonable-length flows, and Sprout is empirically better (at the cost of getting a lot less throughput!).
See, e.g., http://pantheon.stanford.edu/result/1997/ and https://s3.amazonaws.com/stanford-pantheon/real-world/Stanfo...
I guess one key thing to note here is that Salsify is not a "high-bandwidth" transport -- one of the main goals is to wait until the network is ready for a frame (killing off encoder outputs if necessary) to avoid overloading the network and provoking packet loss or queueing delay.
Video over RTP can mean a lot of things, including totally unresponsive traffic that doesn't vary the sending rate in response to congestion signals at all. If an app does this, yeah, life can suck.
I have zero more detail on how they were managing backoff though as this was like 6 years ago with some random video-meeting software that probably doesn't exist anymore (I think there were 100s of video meeting companies that started and died from 2010-2013).