re: Mastodon I see it as the largest use case of the social web today. But there are many others as you well know. We just stood up a peertube instance today for example and I love my pixelfed account. I have been following kbin and Lemmy with lots of interest though reluctant to sign up and engage mostly cause I am worried about spreading myself too thin across all these amazing activitypub services.
This was my point. You shouldn't need an account on all of these services. You should be able to interact from your single Flipboard account. But its likely that, like most new fediverse services, you were testing mostly (or probably solely) against Mastodon. Despite Flipboard having more in common with link aggregators like kbin/lemmy, yall went for mastodon compatibility first.
A lot of people are worried about large orgs/companies like Flipboard/Meta joining the fediverse and controlling it, but Mastodon itself has been in that position for a long time. It's controlled and limited the fediverse for a while and people keep reinforcing its control instead of expanding on the fediverse's plurality.