It's unusual to read that InfluxDB is fast and efficient. Did you try VictoriaMetrics? It usually needs 10x less RAM than InfluxDB for the same workload, especially when the number of active time series is high. It also uses less CPU and disk space on the same production workload. [1]
I've heard of VictoriaMetrics before but haven't had time to play with it. InfluxDB is also now ingrained in a production system so replacing it is not straightforward. The query language is also different meaning everything that uses it will need to be updated too, and coming from a mainly SQL background, PromSQL/MetricsQL looks oddly weird.
Agreed that PromQL and MetricsQL have limited querying capabilities comparing to SQL or InfluxQL. But they cover the most of use cases for analyzing time series measurements, and allow writing much simpler queries than InfluxQL or Flux for these particular cases [1].
[1] https://valyala.medium.com/insert-benchmarks-with-inch-influ...