Sounds like you’re main concern is high availability (HA) and scaling, things Cassandra certainly does well. But if you are also interested in data exploration and complex queries, Cassandra might not be the best choice. I think there is certainly a part of the spectrum here that is not well addressed by something like Cassandra. A future clustering version of TimescaleDB will provide horizontal scale out and solutions for HA, btw.

Also, regarding vacuuming, TimescaleDB does not suffer from it much under the normal workloads it targets because time-series data is largely immutable and deletions typically happen at the chunk level (i.e., dropping complete tables), avoiding any vacuuming during deletes and making wraparound vacuuming more efficient.