No, the throttling is much more aggressive than real time. I suspect it's Google's way of sneakily breaking ancient YouTube clients that won't run arbitrary JS as a countermeasure for downloaders, without really breaking them all the way, so users of e.g. ancient smart TVs just think their network is (unusably) slow instead seeing an outright error, so they don't complain en masse that their TV no longer works properly.

Typical video bitrates for bog standard 1080p30 will be in the 1MB/s range, so the throttling is around 20x slower than real time.

Right: I forgot about the higher end encodings. 50kB/s is a speed similar to that of the "base" 360p ("format 18") - ~100MB every half hour.

Sorry, one detail (cannot edit the former reply): 1080p30 will be in the 1Mbit/s range (not «1MB/s»). That's maybe ~2.5x slower (not 20x).

I played a random 1080p YT video and the player-reported data rate is at least 2.5 MB/s, peaking to 20 MB/s (cca 10 MB/s average). 4K is of course much more than that.

I just took a video as a parameter - a recent engineering animation - and got the following:

  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)...

You're right it's somehow weird. Perhaps the player shows decompressed figures? Check for yourself - right-click on YT video player, show developer/debug info, and there's a chart.

I checked that interface (if you mean the "Stats for nerds"), hence I asked you if you were not by chance reading the "connection speed", which could be the closest to the values you reported and may be misleading to a glance.