Centralized has the fundamental problem of power and choice: witness how facebook, amazon, twitter, Apple, etc. can do whatever they want in their ecosystem. Facebook's users aren't going anywhere, they're essentially trapped if they want to get updates from their "friends", so they'll have to put up with whatever choices the social network makes.
But the biggest power imabance is with developers / publishers. Facebook, Twitter, Amazon, Apple, etc. have all been known to push around their third party publishers, compete with them, and even simply disconnect them whenever they want. Those publishers cannot connect directly with their users without a decentralized login.
And if you're into privacy, you might want to consider how much easier it is for state actors (and hackers) to have backdoors into just one server farm that has everyone's auth information rather than if profiles were stored like the web -- each person could choose their own host.
Distributed auth is possible. What you need is a distributed protocol and reference implementations. Something like OpenID or oAuth is a good start. You can sign up with network X and then use X to auth with other networks. Sadly, xauth was discontinued and everyone assumes Facebook, Twitter et al can be the only OpenID or oAuth providers.
What we need is a new protocol, and that's something we've been working hard on, and have successfully designed.
It doesn't even require you to share your user id, name, etc. with the consumer sites you visit. They can be instantly personalized for you and show you all your friends without knowing who you are. When you are ready, you use oAuth (or something essentially similar) to start building up your profiles in other communities.
No third party can know that user A in community CA authenticated as user B in community CB, unless you sharethat information. You know that thing, "Your friend FooBar is on Instagram as Baz?" That's stuff I might not want everyone to know if Instagram is, say, a porn site. A few years ago, there was a huge uproar about Facebook's "instant personalization" with "trusted partners". Today, it came back and no one cares.
Truth is, we are giving up our power as consumers, and even more so as producers who eventually build our own communities on the back of large, entrenched, centralized communities. Do we really want to centralize power when we see all the bad stuff it can lead to? (Internet 2.0 in India because FB is the only option, Net Neutrality fight because telcos are too centralized, etc.)
I say, once we get the tech right, it can be replicated. After all, bitcoin distributed money. The Web, Email, Git, etc are all distributed. Why not social??