Honestly, I think this is the wrong way of looking at things. The Fediverse isn't really like a single social network that's shattered amongst many instances ... it's more like a bunch of individual, separate hangouts, in the vein of classic forums and IRC chatrooms and fandom websites, which have the ability to talk to each other and share stuff if they want.

It's not so much about "blocking" mastodon.social as not choosing to link up with it - because your instance is a specific community, and actual human social relations thrive when they can choose who they're hanging out with. So you choose to talk to other smaller, more diverse communities that you can actually get to know a good chunk of the people in them, instead of just drinking straight from the firehose that is a big instance.

Federating with another instance is basically two groups of people deciding to hang out together, effectively merging. Federating with mastodon.social means, effectively, merging your community with mastodon.social ... which means submerging it beneath the mass of mastodon.social's much greater activity.

A vibrant Mastodon isn't a more-obtuse recreation of the Twitter experience. Twitter is already Twitter. It's about fostering all the things that Twitter isn't - personal and Dunbar-scaled and locally moderated and diverse.