A counter or a timer is clearly no substitute for a log, that would be an absurd statement for me to have made - which is why I said no such thing.

A span as modelled by OpenTelemetry is a a bag of developer-chosen structured data containing a name, a timestamp and some auto-generated IDs to correlate it with others.

It is effectively an open standard for how to collect good structured logs - although it is currently not commonly pitched that way by either tracing advocates or structured logging advocates.

These are commonly used to create trace waterfalls, but can also be used to derive metrics or simple dev-debug output.

I have used this approach myself to great effect, and also spoken to a number of people who have also found success with such an approach - but currently the momentum of existing approaches (and the fact that traditional logging still works well-enough for most people) has not led to wide adoption