Anecdotal - I took over a small, ill maintained Splunk installation at $JOB-2 and reworked it following Splunks current best-practices and it ran like a top as of when I left that place. Having done that process I'm fully convinced that if you're going to run Splunk on-prem you need a dedicated sysadmin for it that knows Splunk's stack. And that kind of person isn't cheap to hire or keep in that role.