A full node needs to store state to validate transaction.
There are multiple block producers
No need to use a always online TTP, you can run your own node
Not all writers are known (though in practice they are known)
Writers are not trusted, they cannot accept invalid transactions
The public can verify the blockchain.

In practice all writers (mining pools) are known for BTC & ETH, especially the top 80% of writers. The bottom 20% of writers only do so with the "permission" of the top 80%. In EOS & Steem anyone can write a block periodically by simply voting for themselves.