Twitter is centralized platform where people down own their data. We need to think how to make open protocols better in order to improve the decentralized web
As if email is any better? Just because you delete all your mail from your inbox, doesn't mean the requisite copies in your sender/recipient inboxes are deleted. Decentralized doesn't necessarily mean data ownership.
Data ownership is just one aspect. However i don't think twitter is good comparison to email at all. Email is for private communications and twitter is public social network.