I think Prometheus works similar to this with some other tricks like compressing metric names.

OTEL can do gRPC and a storage backend can encode that however it wants. However, I do agree it doesn't seem like efficiency was at the forefront when designing OTEL

These tricks are essential for every database optimized for metrics / logs / traces. For example, you can read on how VictoriaMetrics can compress production metrics to less than a byte per sample (every sample includes metric name, key=value labels, numeric metric value and metric timestamp with millisecond precision). https://faun.pub/victoriametrics-achieving-better-compressio...