I have no way to understand what kind of traffic is being blocked by NSG rules.

Currently, the NSG Flow Logs log what rule is blocking it and the associated conditions, but not the details that matched this condition (which is the meat and potatoes of the log).

I really need to know Source / Destination IP and Source / Destination Protocol & Port to make use of these logs.

This should be included somewhere in the flow logs, or diagnostic logs that go Storage Accounts.