a.k.a. the 90–9–1 principle. Does the Fediverse follow this rule, or are there more creators here as early adopters? Are you a creator, a participator or a lurker?
It depends on the platform. For YouTube that's definitely true, but not for Instagram, Twitter, Reddit, Mastodon, Lemmy or Threads. If It's easier to create content for those platforms, users will create content for those platforms.
I definitely very rarely comment on YouTube videos, it just doesn't seem to be any point it's such an awful interface that it's hard to actually track conversations.
Years ago they used to be a plugin that would replace YouTube comments with Reddit comments - although it seems to have stopped working a very long time ago and being abandoned.
Maybe 1% is a bit too low, but it still definitely applies to all sites you mentioned. Like majority of people don't actively tweet, they just follow people.
Also I wouldn't consider most text posts or reposted memes on Reddit and tweets from random nobodies about some dumb shit that no one else will read as "creating content".