The last bit here is a reach. For starters, Persona uses SSL, so it's encrypted. But more broadly, if you're going to use centralized, third-party authentication mechanism you could do far, far worse than Persona. I'd go so far as to say if your site is implementing its own authentication system, you could do yourself even more damage with a poor implementation.
Your critique seems to missed an important part about Persona's design: "It’s also worth pointing out that we do take certain technical measures to limit the data we collect. We’ve designed Persona so that the identity provider – including the fallback Identity Provider that we run – does not learn your browsing history. We consider that a good security practice, not specifically because of surveillance, but generally because collecting data without a user benefit just creates risk."
Further, the main "centralized" risk would be their default identity provider. If you don't want to use that for your domain, you can provide your own, and host it in another country. In this case, Mozilla's servers aren’t even being contacted when you authenticate.
I know nothing about Persona. I have never used, and I have not read anything about it. But that much is clear to me: the communication between you and the Persona provider can happen very much over an encrypted channel, but the data in the Provider is not encrypted with a key which you only know. The Persona provider has the data in the open (except passwords, which are hashed)
This whole fiasco has shown a weakness in the system which was there all the time, but little acknowledged: it is not about encrypting communications anymore. The eavesdropping risk is well understood and there are technologies available to get rid of it (SSL, SSH tunnels, whatever). But now we need to encrypt the data everywhere. Nobody can be trusted with the data anymore because the government can be accessing that data, and they do not need to eavesdrop: they just need to send a letter and implicitly threaten with litigation and imprisonment to obtain whatever data they want.
This makes the technological solutions much more challenging, and some services can probably not be provided. How does Facebook provide services to their users if the data they have must be encrypted and they can not access it? How to share with friends photos if they are encrypted? Maybe creating ad-hoc group passwords to share data? I do not know, it is difficult.
The only thing those in power would find out by looking at Mozilla's servers in charge with Persona authentication would be your freaking email address and that's it. This is by design.
"It’s also worth pointing out that we do take certain technical measures to limit the data we collect. We’ve designed Persona so that the identity provider – including the fallback Identity Provider that we run – does not learn your browsing history."
That does not say "we only store your email address". It also does not say they are storing more than that, either. In any case, the data is not encrypted, so my argument stands.
"Many sign-in systems carry your profile data with them; some even share that info with other sites and social networks. We believe you should control how your personal information is shared. Persona lets you get started with just your email address; you can add your profile data later, when and where you think it’s appropriate."
Whatever that "profile data" is, can be requested by the government.
The "profile data" that refers to is the profile data you want to add per-site. It's got nothing to do with Persona.
All Persona knows is your email, a password and the fact that you (maybe) want to authenticate at some point (but it doesn't know where, and it can't be sure you're actually trying to authenticate somewhere even).
Your critique seems to missed an important part about Persona's design: "It’s also worth pointing out that we do take certain technical measures to limit the data we collect. We’ve designed Persona so that the identity provider – including the fallback Identity Provider that we run – does not learn your browsing history. We consider that a good security practice, not specifically because of surveillance, but generally because collecting data without a user benefit just creates risk."
Further, the main "centralized" risk would be their default identity provider. If you don't want to use that for your domain, you can provide your own, and host it in another country. In this case, Mozilla's servers aren’t even being contacted when you authenticate.