To offer a different perspective, I think this is lazy criticism. There is a fundamental tradeoff between the "sharding strategy" of a social network and user experience. Both bluesky and mastodon are reasonably pareto-optimal given this tradeoff.

Mastodon goes for real "decentralization" with tiny shards of the "content tier", which means:

1. There is a lot of intra-shard bandwidth but relatively limited inter-shard bandwidth. You can create a truly seamless global experience, with global search, recommendations etc.

2. There is no uniformity in user experience (say moderation-wise) as each shard is essentially a personal fiefdom.

Bluesky instead decouples the storage layer from the caching + serving layer. This allows data portability but still allows a truly unified view of the social network.

Users are free to choose between the two approaches and most overwhelmingly choose Bluesky. But it is not very thoughtful to criticize a pareto-optimal design point for compromising one property to gain another.