I think its more the first line of defense, they are not there to kill, they are there to basically state I don't want you here without provoking a lethal response from whoever is encroaching on them. It causes a lot less death of their males since they are known that they are not a threat, reducing the overall attrition of them over time and making life easier on the hive.
The females with the stingers come out if something is a real threat, ie something messes with the hive or queen.
Honestly, kinda reminds me of British (and other non-militarized) police. Don't send guns to every problem as most can be solved without it and some are made worse by their presence.
I mean if I did not know it was stingless I would still be scared shitless if a handful of them headbutted me. I might even psychologically convince myself that I was feeling stinging pain.
Hah, I have one that likes to just float in front of my shed for some bizarre reason, I always try to avoid it for concern that it could sting but knowing this I may just ignore it now lol, ty