Is there a way to throttle nsurlsessiond/cloudd?
This is not a throttling solution, but can alleviate some problems.
Use Activity monitor, Network tab to find out the PID of nsurlsessiond with User _nsurlsessiond.
In Terminal, run
sudo kill -STOP 1234
where 1234 is the PID you found above.
When you want to run it,
sudo kill -CONT 1234
Make sure you got the correct PID and not stop other crucial processes.