It sounds like maybe you did not setup rclone right. The first thing you must do is this:
Make sure you have setup both Gdrive and Mega as remotes, edit your rclone.conf file and insert this last line of each remote
server_side_across_configs = true
Then you run this command:
rclone copy –drive-server-side-across-configs Gdrive:/Folder Mega:/Folder
Obviously changing Gdrive:/Folder Mega:/Folder to your info
You can see my server side copy stats and rates below.
The images below show you speeds I got without using local network.
I was able to transfer 50TB very quickly doing this.
Keep in mind if you are trying to do more than 750GB you must use service accounts.
In the picture below you see “fatal error” that is because I tell each transfer to stop at 740GB, that way it auto closes the connection and moves on to the next command to keep copying.