I quoted the documentation that claims _something_ is pipelined.

That is extremely vague on what that is and I also didn't check that it's true.

Both the original claim "the issue is the serialization of operations" and the counter-claim all sound like extreme guesswork or me. If you know for certain, please link the relevant code.

Otherwise somebody needs to go check what it actually does; everything else is just speculating "oh surely it's the files" and then people remember stuff that might just be plain wrong.