The photo you posted of the NATHAN STEWART shows most of the bottom crushed in and undoubtedly leaking. The port side pin is missing, but there is little damage to the heavy structure around the pin. Nor would there be fuel tanks in the “pin room” surrounding the pin.
If the tug had been towing astern, the barge would have run up on the tug and crushed it down onto the ledge where it ran aground. There would have been a lot more damage and more spilled oil. Of course, the barge would have also been heavily damaged. Since the barge was empty, probably not much additional spill.
If the tug had been pushing the barge with push wires instead of pins. The wires would probably have parted immediately. The barge would have drifted off and grounde elsewhere.
It may be that the strong pin attachment enabled the barge to drag the boat over the ledge and into deeper water where it then sank. Or a rising tide may have enabled the barge to drag the tug off the ledge.
If it had been a tanker instead of a tug barge combination, with an undamaged empty barge, the salvage would have been a lot more difficult.
Again, I don’t see how the fact that it was an ATB or the pins failing after the grounding contributed to this spill.