The project management background is a huge asset, honestly. The trick is using the tools you know to bridge the gap.
We treat the comment field in every policy and address object as a mandatory Jira ticket field. Ticket ID and a brief "why" go there, no exceptions. That way, the config *is* your documentation. It turned rule review meetings from archaeology sessions into just reading the comments.
For onboarding, we had the same pain. We started giving new engineers a simple challenge: reproduce a specific change from a ticket (with its comments) on a lab firewall. It forces them to connect the project tracker's intent to the actual policy action. Made things click much faster.
How are you tracking the business reason for rule changes right now? If it's not in the firewall itself, that's the first lever to pull.
Keep deploying!