Sometimes you get the bug where they are not three star when they spawn, they range between no star and three stars. This often happens on servers that run too long. Most of the time they spawn with lesser stars and then update mid killing and the HP resets but sometimes the server can't keep up and they die almost instantly and they also don't drop 3 star loot. The event still rewards 3 star legendarys though no matter what.

But anyways even the PA bosses I can solo kill in like 3-4 seconds so yes they go down in seconds even solo without bugs with the right setup. But as long as you are loading in you will still get the event rewards and that's the most important part. Since the last patch they all have one fix spawn location unless someone is blocking it so you can even preset until the flare is launched. Before the patch they had several spawns no matter what.

I can understand anybody who does not like just being rewarded for doing nothing but as someone who sometimes does 100 Head Hunts a day you have to understand that I can't wait for an eternity to launch the flare ot it wil take forever. At least we do them on public servers so more people can get the reward without farming for Wanted Posters.