> A histogram of the duration it took to serve a response to a request, also labelled by successes or errors.

This is so much easier said than done. Most time series db that people use to instrument things quite simply cannot handle histogram data correctly. They make incorrect assumptions about the way roll-ups can happen or they require you to be specific about resolution requirements before you can know them well.

Then histogram data tends to be very expensive to query so it bogs down preventing you from making the kinds of queries that are really valuable for diagnosing performance regressions.

Finally, the visualization systems for histograms are really difficult because you need a third dimension to see them over time. Heat maps accomplish this but are hard to read at times and most dashboard systems don't have great visualization options for "show this time period next to this time period" which is an incredibly common requirement when comparing latency histograms.