You can do this, which will run very quickly:
| tstats count where index=* sourcetype=X by host | sort 0 -count
If you only want to see the top 10 or top 20, replace the zero in the sort command with the number of hosts you would like to see in the results. Note that this is counting the number of events, not the size of the events. So which this may be correlated with license usage, it will be not match. For information on license usage by sourcetype, take a look at the Distributed Monitoring Console (called just the Monitoring Console starting in Splunk 6.5)
I guess you're trying to make a custom license dashboard?
By default, there should be a search called
License Usage Data Cube in your search app. If not, it's this search:
index=_internal source=*license_usage.log* type="Usage" | eval h=if(len(h)=0 OR isnull(h),"(SQUASHED)",h) | eval s=if(len(s)=0 OR isnull(s),"(SQUASHED)",s) | eval idx=if(len(idx)=0 OR isnull(idx),"(UNKNOWN)",idx) | bin _time span=1d | stats sum(b) as b by _time, pool, s, st, h, idx
Accelerate that search using report acceleration and an appropriate time range, e.g. 30 days. Once the acceleration has completed, add the saved search to your dashboard as a base search and display your data with a postprocessing search something like this:
| search st=$st$ | timechart span=1d sum(b) by h
st is a token from a dropdown selecting the sourcetype to filter by.