grpc_req_duration actually also contains the number of requests, you just have to enable count in the summaryTrendStats option. The old http_reqs counter just was added before k6 v0.26.0, when we added the count property of Trend metrics, so we didn’t remove it for backwards compatibility reasons.
The other http_req_* metrics are more complicated. Due to the nature of gRPC calls and the Go libraries we use to make them in k6, it’s not easy (or might not be possible at all) to actually measure all of the distinct times we can measure in HTTP calls 
So we’re currently measuring only the thing we can measure with certainly, how long does the RPC call take.