I think generally, a TTP is going to be more efficient than a system without a TTP. "Trust" at its essence is a shortcut. Without it you have to create a general enforcement mechanism which is going to cost something. E.g., the cost of incenting miners. You can slice it difference ways, but in the end you need the distributed network of nodes to exist and the people who control them to be invested in the continued existence and integrity of the system.
I say "generally" for a reason, because I think it's certainly possible that there are cases where the cost of the third-party is too high or the third-party may not be reliable enough, etc. But generally, it seems to me that blockchain is an inherently inefficient mechanism.
On top of that, the only effective use so far has been to create an investment bubble. Once enough money has been lost on that I think there's a good chance blockchain will get a black eye which will cause people to steer clear even if they may have a use case that's a good fit.