This is bugging me too. Just left an instance which I felt was moving too slowly because 100% of the players gather in one place then 70%-80% of them afk while waiting for the others to pop an NM on that position. They use persistent cheering emotes with the glow sticks while they wait; it's like a meme thing now. I suggested a couple of times for us to split up and farm multiple monster types simultaneously to make use of all players and make more efficient progress to popping NMs, but I didn't sway anyone.

There's actually one specific NM I've never seen because nobody ever works on that one. I hear it's a cerberus type enemy but it's not viable for me to trigger it solo because the drakes in that cave are a few levels above the player cap I think so I at least need 1 party there, not just me alone. Like you said, if I do go off alone somewhere I'll miss the one NM that everybody stacks on because all the afkers return when they hear the fate music and mow it down in 15 seconds. It's always the low/mid level NMs like Serket which people farm on my datacenter, even the players up to the lv20 cap, so I will see those ones 50 times each before I've seen the higher one that I'm interested in but other people aren't.

Somebody in my FC admitted to just going into Eureka to afk and play Nintendo 3DS games while waiting for the one "fate train" NM to pop. She hates the content, but I feel it's the way people are playing which makes them dislike it so much. If people spread around the map, farmed things at their own level range and then courteously waited for arrivals from other parts of the map when their NM spawns, I feel we'd have more fun and progress faster.

I think we at least need better protean gains when playing solo or in a small group just chaining enemies.