Hi physicles, member of the InfluxDB team here. What version of 1.x are you running? Also curious to know if you've tried 2.x.
To be fair, we still haven't paid you guys a dime so I can't complain. But if you're interested in hearing my thoughts I can email you after next week's holiday.
Minor nit on "TSM (not TSI)" - TSM (.tsm files) are the data files and that format hasn't changed. TSI is the newer, although mature at this point, indexing option that spills onto disk and can therefore be larger than the original in-mem index. You're probably using in-mem indexing.
We're always interested in feedback. My name is david. You can email me at <name> at influxdata dot com.