I think you need to sum the data in KB by Host rather than series. Each host has multiple sources and source types. It would be better to monitor the data throughput per host then series. Use the below search query:
index=_internal group=per_sourcetype_thruput | stats sum(kb) as DataKB, avg(kbps) as AVG-KBPS by host | eval DataGB=round(DataKB/1048576,2) | sort DataGB
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