First do not conflate occurrence rate or probability of occurrence with the severity. Severity is severity regardless of the occurrence.
Many downstream manufacturing customers do NOT have tons of inventory. In fact the automotive industry has very severe penalties for 'shutting their lines down'. A single missing part can instigate a line shutdown to determine the extent of the event.
My organization is one of those 'end of the line' manufacturers. The next person downstream from us is the user. We practice Toyota Production System and have very little inventory on hand. If you sent me boxes with missing parts that would be a very serious thing for us. It might not Pose a hazard to our users but it would put you on the non preferred suppliers list if it was a repeating event or if it were a single large event.
Second I make a bold statement that it seems that you are approaching
FMEA as a 'check the box' activity and you might benefit from thinking more about the intent of an FMEA. The intent is to identify areas for improvement mitigation and control. When you start trying to rationalize these opportunities away you are gaming the system. This behavior is anti-quality. Please reconsider your motivation...