I am having same issues now as well where a 200MB 10 minute video is taking over 30 mins to upload.
I have uploaded several files through the API larger than that before and never noticed it feeling this slow. Done in maybe 10 minutes max .
Why are your recommendations in the thread you linked not in the documentation?
I have received incorrect responses from google employees on this forum before so just trying to be sure I can trust what I am reading.
Like this thread that still has no useful advice Files API increase quota beyond 20GB? - #10 by Pooja_Kapse