Yes, those authorities. Either I trust them and fly (ever) or I don't and you never fly. There is no middle ground here. If you fly on the A350 which is also new - you trust the FAA/EASA that they are safe to fly. If I don't trust FAA/EASA, I can never fly the new A350 either. In fact I can't fly on any plane, unless I adopt some strategy of only flying ones that have an established safety record (i.e. old planes). But even with those, I trust the authorities who ensure the training of the pilots is OK, that ATC works etc. They are the same authorities...
They might not always do their job the way I want them to, but there are no other authorities in this case to go to for a second opinion.
I have no capability (nor much of an interest) in even beginning to judge these authorities. That's my point: I trust them blindly because if they turn out to roll dice when making regulation or approving aircraft - it's still better than me doing it.
Now, the situation is a bit special now that there are efffectively TWO competing authorities. It's not that there used to be just one, but that one used to be the authortitive one (or that they spoke with one voice). This complicates things. So OK - when there are conflicting information I might trust the cautious one. But for all practical purposes, these authorities are opaque to the average traveler. I must either trust them or stay on the ground.
They might not always do their job the way I want them to, but there are no other authorities in this case to go to for a second opinion.