The duration metric as recommended by the article, but not broken out by success/failure.

yea that's not good advice, but "don't rely on overstuffed dashboards" is good advice.

you should only have simple dashboards (and alerting) for KPIs and end to end checks. Everything else should be instrumented and debugged using a real time sorting and slicing tool, esp if you have a complex system (microservices, distributed system, polygot persistence).