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.