Subsunk:-
The ACO fleet was grounded because it was expedient to do so for several reasons.
Perhaps, but the only reason that matters is that it was unairworthy. You may well be right that other fleets too are so afflicted but are not grounded for operational reasons, but that doesn't alter the facts re the ACO fleet.
OC 2 FTS made the call as is his prerogative
Not sure what call that is. If it was to ground the ACO fleet then he was merely passing on that command. I assume that it came from the MAA, or doesn't the title Authority mean what it says?