If "yes", then you still don't need blockchain. There are better protocols, like DHT. The only time you need blockchain is when you need to tell which of the two related statements was issued earlier and at the same time you absolutely have to have no trusted third party that assigns timestamps to the statements.

There's another aspect, unforgeability. The interesting thing about the blockchain is that it is a very hard to forge data-set, by design. You can take a proof of work blockchain and look at the hashes of the blocks in it, and based on the number of 0's in each block (the difficulty), you can know how much energy (and cost) went into mining that block.

So if there's a danger of forgery, or you have an interest in security, a blockchain with proof of work provides a really trustworthy way to know you're getting authentic data, because you can look at the chain, and know things like it would cost about 100,000,000 to forge this full history, and 1,000,000 to forge to last block.

Just because each block has had gigawatts of computing power thrown at it doesn't make the block's contents correct, or 'the truth'. Case in point: every stolen bitcoin or ethereum wallet. The blockchain is storing the wrong owner of these coins. Every hack can be considered a forgery, and the miners will happily validate it.

Only if the community does not decide to fork and everyone jumps to the fork like with The DAO. Then maybe you can look up everything in the old branch of your chain but nobody cares...

If any blockchain could be regarded as the truth at any time, why bother with a blockchain at all? Just let a trusted third party run a database. Or vote on its integrity if you wish to distribute trust.

I agree, although I might add "trustless" in there.

i think trustless == ownerless. do you agree?

There's more dimensions to that though. Can participants have identities? If yes, then you don't need proof-of-work, for instance but can have a distributed ledgers with conventional algorithms for Byzantine agreement etc.

Might be just my misinterpretation, but when I hear blockchain I usually just think of conventional totally trustless and identity-less protocols that necessarily require proof-of-work - which is a security level which is not needed for most applications.