I'd beg to differ, honestly. I'd love to see the fediverse take off. We desperately need an alternative to centralised everything where the actions of one company which almost always is profit-motivated can control everything you see and use your data for their own purposes.
I get what you mean by how a smaller community is nice to have, though. But that's also a benefit of the fediverse - you have a small community of your own with it's own culture, while not losing the connection to what's happening outside. And there's some cross-over that makes it easier to talk to others who aren't in your own community, without needing to adapt to their culture first.
Yup, send them a GDPR data request. https://support.reddithelp.com/hc/en-us/articles/360043048352-How-do-I-request-a-copy-of-my-Reddit-data-and-information-