One negative effect of scaling I’ve noticed is that mature social networks (eg Instagram) seem harder to break into. Only established influencer content is surfaced so a new creator has trouble.

TikTok seems much better at promoting newer creators, possibly because it doesn’t have as many large existing creators. This means all the new talent goes there, and then the established talent eventually follows.

TikTok nailed that. It’s well established now but back when it was still growing and sort of small, creators who were on both Instagram and TikTok praised TikTok for how easy it was to break in (with good content and not merely follower count).

I'd love to see actual research on "the uncool participants effect" but anecdotally it feels like a real thing that's impossible to avoid. Any social network will start to favor a specific culture - enforced either by the algorithm or by its participants.

Once that culture starts to go out of fashion (which is inevitable) either the algorithm will have to shift to meet the culture (because the existing participants are probably not going to be fast enough to change) or new users will find another platform to start using. That's why even though people are saying Instagram will die if they start to prioritize Reels, I feel like they're going to die if they don't and this is a last ditch effort.