Concentric
You are spot on. I was chilled to read the number of critical processes that are required. So many opportunities for error.
That process has to happen how many times (eight of those gears) and as you say thats before you mention all the bearings, raceways and other processes.
I dare say if you add up all the processes, from ensuring that no one has a biro in their pocket at the foundary (non melting ball can cause component failure) to design, to regulatory errors, to assembly for all components in series.
Far from saying that these things are safe it is an absolute miracle that they are as safe as they are, showing what an amazingly reliable job all the characters involed are performing despite the whole exercise being so inherently dangerous.
2 crew performing the softest of flying tasks goes some way to
Serial risk of 1000 processes, maybe 10000? Still hoping to acheive 1x10^-9? daft unrealistic nonsense