There is no achievement. Just an entry in your history that nobody is ever going to read.As the event goes on, fewer players show up until no one shows up at all because everyone has the achievement.
Uhm... camping an HNM for hours against other groups IS random. Well, unless someone is botting.this is exactly the kind of nature I wish I'd never find in a mmo event. I'd rather camp for hours a non instanced NM against other groups... at least that's not random.
At least you can't bot a spontaneous GM event.
Lots of games have events that come and go, and In those that I've played, nobody complains about the fact that they exist (Sure, some might talk about how much an individual event may have sucked/not sucked, but they don't complain that they get the events at all). But in FFXIV, everyone feels entitled to be able to have anything and everything how they want, when they want. Look, if these events don't interest you, then don't do them. You are NOT missing out on anything essential or important. These events are largely for fun only.
I have not seen one of these events yet, and it's no big deal to me. If I see one, yay. If not, oh well.