Decentralization by means of replication eliminates the power to control that data entirely, in exchange for dissemination. The way to distance yourself from your posts is the same as on an image board: create a new pseudonymous persona, or maintain no persona at all.

In federated systems, nodes rely less on local stores, so deleting data from a node may work better. It helps make Mastodon/Pleroma confusing and fragmented because instances capriciously block other nodes and users without any signal that's happening. The result is users subscribe to multiple nodes lest their conversions be mangled by getting muted by third parties.

Federated systems could be more friendly and work with users' idea of privacy, but that requires them not to abuse the powers which they abuse now. There's no future for it in wide-spread society, and any smaller group you trust to not abuse it, you can also trust to not abuse your posts.