Sorry @Sisyphusson, I’d just completed my reply as you made yours.
I don’t want to reduce your points to just a single reply, but something to bear in mind is that happens to all games over time. Interest wanes, reduces in scope. The people with the time and availability to put the effort in are the biggest names (assuming they stick with the game itself). The item databases are fully-setup, the fan wikis fully-populated. Adding to that now is easier than it ever has been.
We cannot assume what people do with the information streamers present. We only have anecdotes. I only have anecdotes. Most of my gameplay knowledge comes from a) the game, b) here and c) the item wikis just so I know a bit about the Legendary that just dropped. That’s my personal, singular experience.
I think you’re conflating what happens with a game over time, with the existence of streamers and them being incentivised by the developer (which is a kind of exchange that has happened for years. Decades, just about). Maybe there’s some cross-pollination, but I’d be very wary for putting the blame at the feet of the streamer / incentive mechanic.
So the argument is that they’re monopolising the bandwidth of discussion for any changes made? From who? These forums? Other streamers? How many streamers are there, that aren’t already affiliated with the program?
They have an advantage. They’re not monopolising it. You can’t blame them for social media algorithms. And that still isn’t impacting the game itself. That’s affecting the streamer space around the game.
There are plenty of people that don’t take what the streamers do as holy writ, but even in a universe where this setup didn’t exist, people would still rely on streamers. They’re an embedded part of video game culture and have been for a good decade (I come from an RTS background, which has had people covering various games with video-format content for years).