Now, from a security point of view, it only takes breaking into one issuer to issue bad certificates. But maybe classifying everything as either centralized or decentralized is too simple?
We could describe replication models as centralized or decentralized. Master/master SQL replication is still not decentralized (regardless of whether there are multiple A records or multiple static IPs configured in the client).
With PKI, we choose the convenience of trusting a CA bundle over having to manually check every cert fingerprint.
Whether a particular chain is centralized or decentralized is often bandied about. When there are a few mining pools that effectively choose which changes are accepted, that's not decentralized either.
That there are multiple redundant independent CT logs is a good thing.
How do I, as a concerned user, securely download (and securely mirror?) one or all of the CT logs and verify that none of the record hashes don't depend upon the previous hash? If the browser relies upon a centralized API for checking hash fingerprints, how is that decentralized?
Most people aren't going to do it, but I think that's not really the point, any more than every user needs to review Linux kernel patches. But I wonder if there are enough "eyes" on this and how would we check?