There was an issue turning off throttling at one point:
.901
* Wait for cloud drives to get a disk number before ending async service start.
* [D] Parallelized and optimized drive mounting on initial service start.
* Turning off throttling would not work.
If that's not it, then I haven't seen anything out of the ordinary in my testing over here (I do test all of the providers regularly).
I do have a few FTP servers that are super slow and do cause issues sometimes. But that is entirely server specific. For example, running a local FTP server is blazingly fast.
Google Drive, like in this case, offers sub-100 Mbps downloads (due to throttling), but I am able to stream 4K encoded videos without issues.