It really depends. Capabilities like time-series-specific compression, automatic rollups, complex aggregations and/or ranking, stable storage in S3, clustering, and replication vary a lot and I think that's why we see so many TSDBs out there. I maintain a list of TSDBs[0] and it started as an evaluation of what already available for my previous employer to use. We didn't find one that fit our exact use case, so we ended up building our own on top of MySQL.
[0] https://misfra.me/2016/04/09/tsdb-list/