I have not experienced it, but reviews suggest that the all-American crews have periodic problems with the quality and consistency of their service. It has been a never-ending struggle for NCL since they started the "U.S. Flagged" thing.
I would say there's no difference.
One reason why is that the American workers sign on for a period of months, then switch between the ships when renewing their contracts.
Isin't that the way they all do it? Or are you saying the change in ship at the new contract is mandatory? Most crew members I have talked to spend 1-2 contracts on a ship and then move to another ship.
My point was is that they often switch ships when renewing their contracts, not that they do so with every contract. Because so many do switch ships eventually, neither ship necessarily has better service. That both ships draw crew from the same labor force.