Sure, you can potentially innovate faster, but unless you've got a good way of enforcing your changes on the whole network, one of two things happen. Either you either end up forking the network into multiple islands or building some crazy complex "negotiation" mechanism where two random clients need to agree on what features they support before they communicate.

We saw incompatible islands appear in decentralised systems before (this tends to not be good for users), and we've also seen how any implementation of "protocol/feature negotiation" is basically a disaster for security. I don't currently see how any truly decentralised system is lowering either of these costs.

WhatsApp never used to be e2e for everyone, but they were able to make it universal relatively quickly because it's centralised. All of the poster child decentralised protocols (SMTP, XMPP etc.) are still not e2e for everyone despite decades of effort.

I think in practice it won't be so much about agreeing on a protocol but rather new apps just parasiting off of the data models of the most popular and successful apps.

The thing about decentralization is that it forces the data to be available. So for example Facebook can't stop an alternative app from having full access to Facebook groups even if they want to.

So the big successful apps most likely end up deciding the data model and feature set, and everyone else just borrows that, and if they extend or add features those features won't appear on every interface. Which is okay as long as the common core (determined by the big app) is all there.