Why not a unixish simple tool to handle metrics? assuming $prog outputs log info to stdout: $prog | collect | action and 'collect | action' could all be done somewhat simply with awk and 1000x more portable.
With graphite protocol the metric stream is already plain-text with just 3 fields per line (path value time), its pumped over a socket to a collector.. but that's where the hard stuff starts.
Store it where ever you want, this isn't a magical datastore that makes things faster, use clickhouse-client, whatever it doesn't matter.
There is a widening disconnect between the unix way and how new projects are created.
Logs contain a lot of detail that are not appropriate for metrics. Logs output tends to be expensive, it costs a lot of time and IO to emit, compress, send, store logs. Logs also tend to contain PII things. Usernames, IP addresses, trace IDs, etc. We don't want that kind of cardinality in metrics.
Metrics are another thing. They tend to be internal counters inside a single process. With multi-threaded languages like Go, Java, C++, we can track metric data in memory very efficiently.
For metrics, see https://openmetrics.io/
What you are proposing for deriving metrics from logs exists in plenty of forms. Check out https://github.com/google/mtail , for example. Of course, you still have to store them somewhere, visualize them somehow, etc. That won't simply be part of your shell pipeline.