50 kB/s means you'll be downloading a 10min video like 10 hours.
Very misleading phrasing: you would download in 10 hours a ~10 hours long video, which (of course) could have been downloaded in a fraction of the time.
The throttling has the user download at a speed similar to that required to viewing the video.
format 18 - 640x360 AVC1, V+A : ~50kB/s
format 22 - 1280x720 AVC1, V+A : ~60kB/s
format 137 - 1920x1080 AVC1, V : ~128kB/s
format 400 - 2560x1440 av01, V : ~450kB/s
format 401 - 3840x2160 av01, V : ~850kB/s
Are you sure you are not reporting mega/bits/? When you mention the «player reported data rate», are you sure that is not the "connection speed"? 10MB/s means downloading 36GB/h (one CD per minute, dozens gigabytes per hour)...Typical video bitrates for bog standard 1080p30 will be in the 1MB/s range, so the throttling is around 20x slower than real time.