I’ve had this problem for several months now.
For my home internet connection 400/50mbit upload works as expected but download jumps up and down like crazy with rclone. Now interestingly the official Google Drive Stream app jumps up and down too for download, similar to rclone. But if I try to download the same file in the Drive web interface I saturate my connection everytime.
To let you get an idea about how this looks here are several screencaps from Windows Resource Monitor while copying the same 10gb file:
This behaviour of rclone doesn’t change neither when I change chunk sizes nor when I use the copy command instead of a mount.
Already tried different Computers at my location. tried running rclone in a linux vm. Always the same problem.
Have a remote dedicated server where I have no problems with my rclone mount.
My guess is that it could have something to do with my ISP or my router (that is owned by my isp)? But why would Google Drive Web work then without problems?
As a test, when I routed all my internet traffic through my remote server over VPN I had a steady 20MByte transfer rate with rclone and drive file stream.
Right now I mount the mounted gdrive from my server with winsshfs. And this works good enough for 4k streaming. But thats just a not so pretty workaround.