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I've seen all the things you've described done by a single guild in L2. Literally a huge crowd of people doing the same quests/mobs/locations to optimize their gameplay. And from what I've heard there's some huge alliances of thousands of people out there. And from the pov of a single player, a group of even 100 people running around together, because they're a well-cooperated bunch, would be no different from a streamer and his posse existing on a server.
Except the streamer would most likely got no clue what he's doing or where he's going, while the guild would most likely know the best paths and would be present at all the juicy spots on the map.
But even outside of that, the world is huge and there's no TPs AND you can go wherever because at release all locations are lowlevel, so it's not like the streamer group would stop you from doing anything in the game.
In other words, that shit looks the same to me. Except cooperated huge guilds have much bigger impact on the core gameplay of the game because they're optimized out of their minds and work towards singular goals, while streamer just fucks around with a few hundred dumbasses running around them. And if a huge guild leaves a server, imo, impact of their leave would be bigger than a streamer's, even if both would definitely have an impact.