Conceptually I get what you're saying, but I've never used Twitter and I dropped Reddit in July cold turkey.
I have had no issues being where the people are just sticking to the Fediverse.
I don't feel like I've missed anything. I did pick up Mastodon, but that's just lurking. I picked up a few news apps to fill in a blank or two, but those usually end up on Lemmy anyway.