But using one instance to handle voting/replies means it's centralized (everything happens in one place). Lemmy doesn't allow someone to edit content from diff

But using one instance to handle voting/replies means it's centralized (everything happens in one place). Lemmy doesn't allow someone to edit content from different instances so that aspect isn't decentralized. If I make a post on one instance the post could be shared within the federation which makes that feature decentralized. At best Lemmy is a hybrid decentralized-centralized application.