> I don’t think this is true in practice. On the whole, I suspect the ordinary user of email is exactly as centralized as the ordinary user of Signal.

Not true, because an open standard will always be superior to a company-owned (and controlled) app.

I run all my own email infrastructure. Many of my friends do. We can communicate without any corporate overlord deciding who can say what.

Signal is a company, one that demands a phone number to use their proprietary service and can shut you out in a nanosecond. No thanks.

Signal is not a company but a non profit, and their service is not proprietary but fully open source including the server side. That being said, it is centralized and so less resilient, it can be taken down more easily. So you have to pick between more secure (Signal) or more resilient because decentralized (DeltaChat). Theoretically Matrix has both, but at the moment it is not as secure as Signal, and its UX is clearly worst. And to that you have to add the complexity of decentralization for normal people: which server to pick, how can I know if someone I know has an account... Here the comparison with email should help but still it is not as easy as entering a phone number and immediately you have all your contacts available.