I would take a different approach.
Engagement metrics are great, but they don’t get to the heart of what people are coming to your experience for in the first place.
They are proxies for what the visitor values.
e.g. in pharmaceutical marketing the ‘user’ is often a medical professional and they join the experience because they want to ‘learn’ something (e.g. the correct monitoring for a cancer patient). If we want to understand if we built something valuable that the medical professionals would care about we measure what they value = if they are ‘learning’ something.
I would argue that we could question more if we need to use proxies for value or if we can just measure the value instead?
This is a great article on the topic: https://hbr.org/2020/04/the-most-important-metrics-youre-not-tracking-yet