Thinking escrow services make them a central bank means you're misunderstanding a lot of things. "Central banks" control currency printing, which silk road never did. The entire point of BTC is that being algorithmically controlled. I suspect you just mean traditional banks where people have their checking and savings accounts. But you're still mistaken. Having an arbiter for the money involved in one transaction does not mean you can have all of your funds frozen. At worst you can have a bad arbiter that awards the money from one transaction unfairly. They also absolutely can not "reverse transactions" if you are paying with a transfer on chain. I think you're mixing up "escrow" where a website requires you send them your BTC and they transfer your BTC to someone else for you by moving numbers in a SQL table with actual on chain transactions. With on chain escrow the arbiter can never get the funds, only forward them or send them back.