Yes, it really does!
Since my post yesterday, lemmy.world has added about new 2600 users, bringing the user count to 28361 users. It's the clear second-largest lemmy instance out there and quickly closing in on lemmy.ml's 36k users (not taking new signups).
Interestingly, third-largest lemmy instance beehaw.org seems to have lost about 275 users since yesterday. Guessing some people were pissed off about its defederation enough to delete their beehaw accounts?
The fact that Lemmy can federate is an advantage on its own, even if in practice we mostly don't. A federated Reddit wouldn't have had to resort to the blackout; users could have spun up their own instances, defederated from the central instance, and carried on, cutting the problematic management out with very little actual loss to the rest of the community. Even if a single instance ends up dominating, the possibility of federation is a big win for users.