Many of the issues I see people outline come down to defederation and lack of centralization, but I’d argue those are features rather than bugs.

This is exactly what I mean. These aren't dealbreakers, but there are downsides to the way that it's structured - namely, admins of larger instances making decisions on the behalf of their members that you may not agree with and the relative complication of discovering new communities on other instances compared to Reddit. Reddit had its own issues inherent to its platform (first-come-first-serve with regard to community names, aggressive attempts at monetization), and I think this one will be better off in terms of management because of the decentralized structure, but that same decentralized structure may put off new users and make it harder to grow.